Post on 26-Jun-2020
THEORY OF ELECTRON-MOLECULE COLLISIONS
FOR ASTROPHYSICS, BIOPHYSICS AND LOW TEMPERATURE PLASMAS:
OPPORTUNITIES AND CHALLENGES
December 3-5, 2012
ORGANIZERS: Viatcheslav Kokoouline, University of Central Florida Chris Greene, Purdue University
Sponsored by:
Institute for Theoretical Atomic, Molecular and Optical Physics*
Harvard - Smithsonian Center for Astrophysics
60 Garden St., Cambridge, MA
http://www.cfa.harvard.edu/itamp/Theory-of-Electron-2012.html
Abstract Booklet and Program
*Sponsored by National Science Foundation
Molecular Frame Photoelectron Angular Distribution of Carbon K-shell in C2H4 Courtesy of Douguet, Kokoouline, Fonseca dos Santos, Rescigno and Orel
TABLE OF CONTENTS
1
TABLE OF CONTENTS PARTICIPANTS .......................................................................................................................................................... 3
PROGRAM ................................................................................................................................................................... 5
ABSTRACTS
DATA NEEDS OF ELECTRON-MOLECULE COLLISIONS IN FUSION APPLICATIONS ........................................ 7
H.K. CHUNG AND B.J. BRAAMS
TIME-RESOLVED MOLECULAR FRAME PHOTOELECTRON ANGULAR DISTRIBUTION (MFPAD) IN
ACETYLENE AND ETHYLENE ISOMERIZATIONS /SIMPLE MODEL TO DESCRIBE THE DISSOCIATIVE
RECOMBINATION OF POLYATOMIC IONS OF ASTROPHYSICAL INTEREST ................................................. 8 N. DOUGUET, V. KOKOOULINE, S. FONSECA DOS SANTOS, T. N. RESCIGNO, A. E. OREL
THEORY OF DISSOCIATIVE ELECTRON ATTACHMENT: BIOMOLECULES AND CLUSTERS ...................... 10
ILYA I. FABRIKANT
SIMPLIFIED MODEL TO DESCRIBE THE DISSOCIATIVE RECOMBINATION OF POLYATOMIC IONS OF
ASTROPHYSICAL INTEREST ....................................................................................................................... 12 S. FONSECA DOS SANTOS, N. DOUGUET, V. KOKOOULINE, A. E. OREL
THEORETICAL STUDIES OF DISSOCIATIVE RECOMBINATION ................................................................. 13
STEVEN L. GUBERMAN
SUCCESSES AND CHALLENGES OF FRAME TRANSFORMATION THEORY ................................................. 15
CHRIS H. GREENE
THE R-MATRIX METHOD FOR ATTOSECOND SPECTROSCOPY ............................................................... 16 A. G. HARVEY, F. MORALES, O. SMIRNOVA
ANGULAR DEPENDENCE OF DISSOCIATIVE ELECTRON ATTACHMENT TO METHANOL ........................ 18
DANIEL J. HAXTON
DISSOCIATIVE RECOMBINATION AND ELECTRON ATTACHMENT IN THE INTERSTELLAR MEDIUM ..... 19
ERIC HERBST
THEORETICAL METHODS FOR TREATING STABLE ANIONS FOR WHICH THE EXCESS ELECTRON DOES
NOT BIND IN THE HARTREE-FOCK APPROXIMATION ............................................................................. 20 K. D. JORDAN AND V. VOORA
ANALYTIC THREE-CHANNEL MODEL FOR RESONANCE-AVERAGED DIRECT AND INDIRECT
DISSOCIATIVE RECOMBINATION PROCESSES OF MOLECULAR IONS ...................................................... 21 I. F. SCHNEIDER, N. POP, AND CH. JUNGEN
RADIATIVE ELECTRON ATTACHMENT TO MOLECULES OF ASTROPHYSICAL INTEREST. BENCHMARK
STUDY OF CN-……………………………………………………………………………………………………………. 22
KOKOOULINE, N. DOUGUET, S. FONSECA DOS SANTOS, O. DULIEU, M. RAOULT, A. E. OREL
DISSOCIATIVE RECOMBINATION MEASUREMENTS.AT ION STORAGE RINGS: ACHIEVEMENTS AND
PERSPECTIVES ............................................................................................................................................ 24 HOLGER KRECKEL
TABLE OF CONTENTS
2
COMPLEX-SCALED EQUATION-OF-MOTION COUPLED-CLUSTER METHOD WITH SINGLE AND DOUBLE
SUBSTITUTIONS FOR AUTOIONIZING EXCITED STATES: THEORY, IMPLEMENTATION,
AND EXAMPLES ........................................................................................................................................... 25 ANNA KRYLOV
PHOTOIONIZATION IN THE MOLECULAR FRAME ..................................................................................... 26 ROBERT R. LUCCHESE
MOLECULAR ANIONS IN THE LABORATORY AND IN SPACE ..................................................................... 27 MICHAEL C. MCCARTHY
LOW-ENERGY ELECTRON-MOLECULE COLLISIONS WITH THE SCHWINGER MULTICHANNEL
METHOD† ................................................................................................................................................... 28 VINCENT MCKOY
VERY LOW-ENERGY ELECTRON-INDUCED DAMAGE OF DNA ................................................................ 29 THOMAS M. ORLANDO
THE DYNAMICS OF RESONANT ELECTRON COLLISIONS WITH CARBON DIOXIDE ................................. 31
T.N. RESCIGNO
COMPLEX GENERALIZED HARTREE-FOCK ............................................................................................... 32 ERIC J. SUNDSTROM, DAVID SMALL, AND MARTIN HEAD-GORDON
R-MATRIX AND VIBRATIONAL FRAME TRANSFORMATION IN STUDIES OF MOLECULAR
PHOTODETACHMENT ................................................................................................................................. 33
MICHAL TARANA AND CHRIS H.GREENE
BOUND AND CONTINUUM STATES IN ELECTRON – MOLECULE COLLISIONS USING THE R-MATRIX
METHOD ..................................................................................................................................................... 34 JONATHAN TENNYSON
DESIREE: A UNIQUE CRYOGENIC ELECTROSTATIC STORAGE RING FOR MERGED ION-BEAMS
STUDIES ...................................................................................................................................................... 36 R. D. THOMAS
PARTICIPANTS
3
H-K. Chung International Atomic Energy Agency Vienna, Austria H.Chung@laea.org
Alex Harvey Max Born Institute Berlin, Germany
alex.harvey@mbi-berlin.de
Alexander Dalgarno Harvard Smithsonian CFA Cambridge, MA adalgarno@Cfa.harvard.edu
Eric Herbst University of Virginia Charlottesville, VA
eh2ef@virginia.edu
Nicholas Douguet University of Central Florida Orlando, Florida
douguet@physics.ucf.edu
Christian Jungen University of Paris XI Paris, France
christian.jungen@lac.u-psud.fr
Ilya Fabrikant University of Nebraska Lincoln, Nebraska
ifabrikant@unl.edu
Kenneth D. Jordan University of Pittsburg Pittsburgh, PA jordan@imap.pitt.edu
Samantha Fonseca Dos Santos University of California Davis, California sfonseca@usdavis.edu
Jobin Jose Texas A&M College Station, TX jlopez@chem.tamu.edu
Tom Gorczyca Western Michigan University Kalamazoo, Michigan Gorczyca@wmich.edu
Viatcheslav Kokoouline University of Central Florida Orlando, Florida Viatcheslav.Kokoouline@ucf.edu
Chris H. Greene Purdue University West Lafayette, Indiana Chris.greene.jila@gmail.com
Holger Kreckel
Max Planck Institute Heidelberg Germany holger.kreckel@mpi-hd.mpg.de
Steven Guberman Institute for Scientific Research Winchester, MA
slg@sci.org
Anna Krylov University of Southern CA, Los Angeles, CA
krylov@usc.edu
Daniel Haxton Lawrence Berkeley Natl. Laboratory Davis, California
danhax@gmail.com
Jesus Lopez-Dominguez Texas A&M College Station, TX jobin.jose@mail.chem.tamu.edu
PARTICIPANTS
4
Robert Lucchese Texas A&M College Station, TX
lucchese@chem.tamu.edu
Hossein Sadeghpour Harvard Smithsonian CFA Cambridge, MA hrs@cfa.harvard.edu
Mike McCarthy Harvard Smithsonian CFA Cambridge, MA
mmcarthy@cfa.harvard.edu
Eric Jon Sundstrom University of California Berkeley, CA
esundstr@gmail.com
Vincent McKoy California Institute of Technology Pasadena, CA
mckoy@caltech.edu
Michal Tarana Purdue University West Lafayette, Indiana michal.tarana@jila.colorado.edu
Ann Orel University of California Davis, CA
aeorel@ucdavis.edu
Jonathan Tennyson University College London London j.tennyson@ucl.ac.uk
Thomas Orlando
Georgia Institute of Technology Atlanta, GA
thomas.orlando@chemistry.gatech.edu
Rich Thomas University of Stockholm Sweden rdt@fysik.su.se
Thomas Rescigno Lawrence Berkeley Natl. Laboratory Berkeley, CA
tnresigno@lbl.gov
Patrick Thaddeus Harvard Smithsonian CFA Cambridge, MA, pthaddeus@cfa.harvard.edu
PROGRAM
5
Theory of Electron-Molecule Collisions
PROGRAM
Monday, December 3, 2012 Phillips Auditorium
8:30 Morning Coffee
Session I Chair: Viatcheslav Kokoouline
8:45–09:00 Introductory Remarks and Welcome
09:00–09:40 Hyun-Kyung Chung, “Data needs of electron-molecule collisions in fusion applications”
09:40–10:20 Thomas M. Orlando, “Very low-energy electron-induced damage of DNA”
10:20–11:50 Coffee Break
10:50–11:30 Richard D. Thomas, “DESIREE: a unique cryogenic electrostatic storage ring for merged ion-beams studies”
11:30–12:15 Holger Kreckel, “Dissociative recombination measurements at ion storage rings: achievements and perspectives”
12:15–2:00 Lunch Break
Session II Chair: Chris Greene
02:00–2:40 Robert R. Lucchese, “Photoionization in the molecular frame”
02:40–3:20 Vincent McKoy, “Low-energy electron-molecule collisions with the Schwinger multichannel method”
03:20–3:50 Coffee Break
03:50–4:30 Tom N. Rescigno, “The dynamics of resonant electron collisions with carbon dioxide”
04:30-5:10 Ilya I. Fabrikant, “Theory of dissociative electron attachment: Biomolecules and clusters”
5:30 Reception
Tuesday, December 4, 2012 Phillips Auditorium
08:30 Morning Coffee
Session III Chair: Tom N. Rescigno
09:00–09:40 Eric Herbst, “Dissociative recombination and electron attachment in the interstellar medium”
09:40–10:20 Michael C. McCarthy, “Molecular anions in the laboratory and in space”
PROGRAM
6
10:20–10:50 Coffee Break
10:50-11:30 Ken D. Jordan, “Theoretical methods for treating stable anions for which the excess electron does not bind in the Hartree-Fock approximation”
11:30-12:15 Jonathan Tennyson, “Bound and continuum states in electron – molecule collisions using the R-matrix method”
12:15-2:00 Lunch Break
Session IV Chair: Ann Orel
2:00:2:40 Chris H. Greene, “Successes and challenges of frame transformation theory”
2:40:3:20 Michal Tarana, “R-matrix and Vibrational Frame Transformation in Studies of Molecular Photodetachment”
3:20-3:50 Coffee Break
3:50-4:30 Anna Krylov, “Complex-scaled equation-of-motion coupled-cluster method with single and double substitutions for autoionizing excited states: Theory, implementation, and examples”
4:30-5:10 Eric J. Sundstrom, “Complex generalized Hartree-Fock”
Wednesday, December 5, 2012 Phillips Auditorium
8:30-9:00 Morning Coffee
Session V Chair: Ilya Fabrikant
9:00-09:40 Christian Jungen, “Analytic three-channel model for resonance-averaged direct and indirect dissociative recombination processes of molecular ions”
09:40–10:20 Steven L. Guberman, “Theoretical studies of dissociative recombination”
10:20-10:50 Coffee Break
10:50- 11:30 Nicolas Douguet “Time-resolved molecular frame photoelectron angular distribution (MFPAD) in acetylene and ethylene isomerizations”
10:30–12:15 Samantha Fonseca dos Santos, “Simplified model to describe the dissociative recombination of polyatomic ions of astrophysical interest”
12:15-2:00 Lunch Break
2:00:2:40 Daniel J.Haxton, “Angular dependence of dissociative electron attachment to methanol”
2:40:3:20 Alex G. Harvey, “The R-matrix method for attosecond spectroscopy”
3:20-4:00 Viatcheslav Kokoouline “Radiative electron attachment to molecules of astrophysical interest. Benchmark study of CN-”
4:00 Meeting Adjourn
ABSTRACTS
7
Data Needs of Electron-Molecule Collisions In Fusion Applications
H. K. Chung and B. J. Braams
International Atomic Energy Agency, Austria
The divertor of a magnetic confinement fusion experiment plays a critical
role in particle control (pumping of impurities and in a reactor also helium ash) and
the control of high heat load. Plasma is relatively cold and dense in this region since
the plasma interacts with a material boundary. In a part of the region, the plasma
makes a transition to a neutral gas or hydrogen molecules are formed on the walls
and under some conditions also by volume recombination. Molecular processes and
interaction of the plasma electrons and ions with molecules and molecular ions are
critical features of the divertor plasma and their correct treatment, together with
plasma-wall interaction, is important in edge and divertor plasma modelling.
Since 1978, the atomic and molecular (A+M) data unit of the International
Atomic Energy Agency (IAEA) has coordinated international activities to review
progress and achievements in the production of atomic, molecular and plasma-
surface interaction (AM/PSI) data for fusion program, and to encourage
international cooperation in measurement, compilation and evaluation of AM/PSI
data for fusion. The unit organizes coordinate research projects (CRPs) to increase
capabilities of Member States to undertake fusion plasma modelling and simulation
of present and future experiments and reactor designs. In this workshop, the critical
needs of electron-molecule collision data required by fusion modeling will be
described and the current and future activities of the unit on compilation,
production and evaluation of those data will be presented.
ABSTRACTS
8
Time-Resolved Molecular Frame Photoelectron Angular Distribution (MFPAD) in Acetylene and
Ethylene Isomerizations /Simple Model to Describe The Dissociative Recombination of Polyatomic Ions
of Astrophysical Interest
N. Douguet1, V. Kokoouline2, S. Fonseca dos Santos1, T. N. Rescigno3,
A. E. Orel1
Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, CA
956162 Department of Physics, University of Central Florida, Orlando, FL 32816
Lawrence Berkeley National Laboratory, Berkeley, CA 94720
In the first part of this talk, I will discuss how chemical reactions can be
imaged by detection of a photoelectron in the molecular fixed body-frame, following
either valence or K-shell photoionization. These two techniques will be contrasted
considering the isomerization of the acetylene monocation (C2H2+) towards its
vinylidene final structure. Several MFPADs at the most important geometries and
for different photon energies will be presented. Another example of K-shell
photoisomerization will be treated, considering neutral ethylene (C2H4).
Corresponding MFPADs at the main geometries of C2H4, as well as comparison with
available experimental data on ethylene ground state will be given .
In the second part of the talk, I will present theoretical results on the
dissociative recombination of many polyatomic ions of astrophysical interest. Using
a simplified treatment, which captures the key ingredients of the indirect
recombination mechanism, we have obtained theoretical cross sections at low
incoming electron energy in good agreement with available experimental data for
large polyatomic ions, such as H3+, CH3
+, H3O+, HCNH+, NH4+
and N2H+. New
perspectives on the very low energy dissociative recombination of HCO+ will also be
discussed, including the possible role of HOC+ in storage ring experimental results .
ABSTRACTS
9
(a)
(b)
The above figure (a) shows the
averaged carbon K-shell MFPAD of
C2H4 at its twisted geometry (b) in
D2d symmetry. The MFPAD seems to
image the molecular geometry.
The upper panel shows the Jahn-Teller splitting
of triply degenerate states of NH4+
by distortion
along one of its triply degenerate normal mode.
This splitting is responsible for the high
calculated DR cross section (lower panel) in
good agreement with experiments.
This work is supported by the DOE Office of Basic Energy Science and the
National Science Foundation, Grant No's PHY-08-55092 and PHY-08-55622.
ABSTRACTS
10
Theory of Dissociative Electron Attachment: Biomolecules and Clusters
Ilya I. Fabrikant
Department of Physics and Astronomy,
University of Nebraska-Lincoln, Lincoln, NE 68588, USA
Recent renewed interest to the dissociative electron attachment (DEA)
processes has been stimulated by the role of low-energy electrons in radiation
damage and ion-beam cancer therapy. In the present paper we discuss electron-
induced hydrogen loss in a few simple biological molecules: formic acid [1], uracil
[2], thymine, and aminobutanoic acid [3]. The DEA process in these systems is
controlled by shape resonances of the A1 symmetry whose width is very large. Due
to the long-range (dipolar and polarization) interaction between the incoming
electron and the molecule sharp vibrational Feshbach resonances and threshold
cusps appear at the vibrational excitation thresholds.
For practical applications to radiation damage it is important to know how
DEA processes are modified in condensed-matter environments. To answer this
question, we use two approaches:
first, we investigate effects of clusterization, in particular how the DEA
process is affected if the attaching molecule is placed in a water cluster environment
[4]. Second, we study how the DEA rate is affected if the molecule is placed on a
surface. The condensed-matter effects can lead to a strong enhancement of the
attachment rates, but, on the other hand, they suppress vibrational Feshbach
resonance effects [5].
This work was done in collaboration with P. D. Burrow and G. A. Gallup
(UNL), V. Vizcaino and S. Denifl (University of Innsbruck), and J. Gorfinkiel (The
Open University, UK), and supporteed by the US National Science Foundation.
ABSTRACTS
11
REFERENCES [1] G. A. GALLUP, P. D. BURROW, I. I. FABRIKANT, PHYS. REV. A 79, 042701 (2009). [2] G. A. GALLUP AND I. I. FABRIKANT, PHYS. REV. A 83, 012706 (2011). [3] V. VIZCAINO, B. PUSCHNIGG, S. E. HUBER, M. PROBST, I. I. FABRIKANT, G. A. GALLUP, E.
ILLENBERGER, P. SCHEIER, S. DENIFL, NEW J. PHYS. 14, 043017 (2012). [4] I. I. FABRIKANT, S. CAPRASECCA, G. A. GALLUP, J. D. GORFINKIEL, J. CHEM. PHYS.136, 184301
(2012). [5] I. I. FABRIKANT, J. PHYS. B 44, 225202 (2011).
ABSTRACTS
12
Simplified Model to Describe the Dissociative Recombination of Polyatomic Ions of
Astrophysical Interest
S. Fonseca dos Santos1, N. Douguet1, V. Kokoouline2, A. E. Orel1
1Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, CA 2Department of Physics, University of Central Florida, Orlando, FL 32816
We present theoretical results on the dissociative recombination (DR) of
many polyatomic ions H3+, CH3
+, H30+, HCNH+, NH4+, HCO+ and N2H+
. Besides their
astrophysical importance, they also share the characteristic that at low electronic
impact energies their DR process happens via the indirect DR mechanism. Applying
a general simplified model based on multichannel quantum defect theory that
accounts for all the main ingredients of indirect DR we calculated cross sections and
DR rates for these ions. Our results, as illustrated in Figs. 1 and 2, are in good
agreement with available experimental data.
Fig.1 – DR cross section of N2H+
Experimental data digitalized from
Geppert et al., Astrophys J 609, 459
(2004)
Fig.2 – DR cross section of H3+ Comparison between
experiments (CRYRING and TSR) and different levels
of theory of our group: a complete treatment (Fonseca
dos Santos et. al.) and the simplified model (Douguet
et.al.).
This work is supported by the DOE Office of Basic Energy Science and the National Science
Foundation, Grant No's PHY-08-55092 and PHY-08-55622 and NSF Grant No. PHY-08-55092.
ABSTRACTS
13
Theoretical Studies of Dissociative Recombination
Steven L. Guberman
Institute for Scientific Research
A long term aim of dissociative recombination research has been to find
agreement between theoretical and experimental total cross sections to at least
better than 20%. This goal has remained elusive and has not been achieved at low
electron energies for any molecular ion, including the simplest, H+2. Both theory and
experiment have made robust contributions to this disagreement. In this talk, I will
discuss recent theoretical calculations of dissociative recombination cross sections
for N+2. I will not show high resolution agreement with experiment because there are
no high resolution experimental cross sections for N+2 . However, I will show that
one must include minor dissociative channels [Guberman, 2012] if one is to obtain
agreement with a future experimental N+2. cross section which has a well
characterized ion electronic and vibrational population. An early storage ring
experiment [Peterson et al., 1998], restricted to “zero” electron energy, found that
the dissociative recombination rate constants for the lowest three ion vibrational
levels are quite similar in magnitude. The theoretical results agree with experiment
at low electron temperature but the theory finds that above room temperature, the
rate constant for v = 0 departs significantly from those for v > 0. The results are
important for ionospheric models at Earth [Fox and Dalgarno, 1985] and Mars [Fox
and Dalgarno, 1983; Fox and Hać, 1997] where the electron temperature is above
300 K and considerable N+2. vibrational excitation is present. Lastly, in a recent
storage ring experiment (Vigren et al., 2012) on HN+2. , an incorrectly derived rate
constant was attributed to contamination of the ion beam with 15N14N+. Did they get
it right?
ABSTRACTS
14
REFERENCES FOX, J. L. AND A. DALGARNO, J. GEOPHYS. RES. 88, 9027 (1983) FOX, J. L. AND A. DALGARNO, J. GEOPHYS. RES. 90, 7557 (1985) FOX, J. L. AND A. HAĆ, J. GEOPHYS. RES. 102, NO. E4, 9191 (1997). GUBERMAN, S. L., J. CHEM. PHYS. 137, 074309 (2012). PETERSEN, J. R., A. LE PADELLEC, H. DANARED, G. H. DUNN, M. LARSSON, Ǻ. LARSON, R. PEVERALL, C. STRÖMHOLM, S. ROSÉN, M. AF UGGLAS AND W. J. VAN DER ZANDE, J. CHEM. PHYS. 108, 1978 (1998). VIGREN, E., V. ZHAUNERCHYK, M. HAMBERG, M. KAMINSKA, J. SEMANIAK, M. AF UGGLAS, M. LARSSON, R. D. THOMAS AND W. D. GEPPERT, AP. J. 757, 34 (2012)
ABSTRACTS
15
Successes and Challenges of Frame Transformation Theory
Chris H. Greene
Purdue University, West Lafayette, IN 47907
This talk will give an overview of frame transformation theory, emphasizing
its application to electron-molecule collisions and especially the coupling between
electronic degrees of freedom with molecular rotation, vibration, and dissociation.
While the theory has had numerous successes, there remain problem areas that are
ripe for improvement and further development. Headway in strengthening ab initio
theoretical treatments of the electronic continuum states of molecules could be
decisive for making progress in this area.
ABSTRACTS
16
The R-Matrix Method for Attosecond Spectroscopy
A. G. Harvey, F. Morales, O. Smirnova
Max-Born-Institut, Max-Born Straße 2A, D-12489 Berlin, Germany
The advent of new XUV light sources such as free electron lasers, and the
development of high harmonic emission both as a light source and as a direct probe,
coupled with advances in detector technology and the laser alignment of molecules,
has opened up the possibility of observation, initiation and control of the fastest
molecular processes. Exposing aligned molecules to these short, femtosecond to
sub-femtosecond pulses leads to ionisation, and the angular distribution of ejected
electrons encodes information about the parent molecule [1,2]. High harmonic
emission from molecules can also encode information abou molecular structure and
dynamics [3,4].
The theoretical descriptions of both of these types of experiment need high
quality dipole matrix elements. They are used to calculate molecular frame
photoelectron angular distributions and in the recombination step of current,
sophisticated, models of HHG [5]. With this in mind we have converted the UK R-
matrix scattering codes [6,7] to treat photoionisation (or recombination) from
aligned molecules.
The molecular R-matrix method is a powerful, multichannel, ab initio
technique for treating electron-molecule interactions. It works by dividing the
configuration space of the molecule into an inner and outer region and making
different levels of approximation in each. The inner region rigorously takes into
account electron-electron effects such as exchange, correlation and polarisation and
in the outer region the electron moves in the long range, multipole potential of the
parent molecule. Matching to known asymptotic boundary conditions gives the
wavefunction representing the ionised molecule plus continuum electron.
Transition dipole matrix elements between this wavefunction and the inital bound
state of the molecule are produced, from which the desired photoionisation
observables may be obtained.
ABSTRACTS
17
We present the first application of our codes and compare with new
experimental data for the CO2 molecule [8,9].
REFERENCES [1] FOR A RECENT REVIEW SEE K. L. RAID, MOLECULAR PHYSICS, 3, 131, (2012).
[2] A. ROUZEE, ET AL., J. PHYS. B, 45, 074016, (2011).
[3] O. SMIRNOVA, ET AL., NATURE 460, 972–977, (2009).
[4] S. HAESSLER, ET AL., NATURE PHYSICS 6, 200 - 206, (2010) .
[5] SEE E.G. A. T. LE, ET AL., PHYS. REV. A 80, 013401, (2009).
[6] J.M. CARR, ET AL., EURO. J. PHYS. D, 66, 58 (2012).
[7] A. G. HARVEY AND J. TENNYSON, IN QUANTUM DYNAMIC IMAGING, A.D. BANDRUK AND M. IVANOV
(EDS.), SPRINGER 55-70 (2011).
[8] H. RUF, R. CIREASA, C. HANDSCHIN, V. BLANCHET, B. FABRE, S. WEBER, D. DESCAMPS, S. PETIT
F. MORALES, A. HARVEY, M. RICHTER, M. IVANOV, O. SMIRNOVA, Y. MAIRESSE (TO BE PUBLISHED).
[9] A. ROUZÉE, A. G. HARVEY, F. KELKENSBERG, W. SIU, G. GADEMANN, O. SMIRNOVA, M. J. J. VRAKKING
(TO BE PUBLISHED).
ABSTRACTS
18
Angular Dependence of Dissociative Electron Attachment to Methanol
Daniel J. Haxton
Lawrence Berkeley National Lab
I will show calculations on the angular dependence of dissociative electron
attachment to methanol, via the lowest, ~6eV A’’ resonance, obtained through fixed
nuclei calculations using the complex Kohn method. I do not consider the dynamics
after attachment and instead use the fixed nuclei attachment probabilities, averaged
over vibrational modes, to obtain the angular dependence prediction as a function of
recoil angles. These calculations are compared with the experiment of Adaniya,
Slaughter, Belkacem et al. at LBNL. The agreement between experiment and theory
is not excellent, but does indicate that the recoil angle of the hydrogen is most likely
about 15 degrees from axial, on average.
ABSTRACTS
19
Dissociative Recombination and Electron Attachment in the Interstellar Medium
Eric Herbst
Departments of Chemistry and Astronomy, University of Virginia Charlottesville, VA 22904, USA
Dissociative recombination and electron attachment are important
processes in the dense interstellar medium, especially in cold regions, where the
gas-phase chemistry is known to be dominated by ionic processes, and star
formation has not yet heated up the gas and dust. Observations from the far-
infrared satellite Herschel towards the star-forming region known as Orion KL
indicate, however, that dissociative recombination plays a key role even in warm
regions. In the hot outflow source in front of Orion KL, the unusual ions OH+ and
H2O+ are both present in high abundance despite the fact that they react with
molecular hydrogen, the most abundant species in the gas. On the other hand the
saturated ion H3O+ is not detected. To understand this unusual phenomenon, a
model with a very high rate of ionization caused mainly by far ultra-violet radiation
is advocated in which dissociative recombination competes with hydrogenation.
Observations from the ground show that molecular anions are present in a number
of different cold and “lukewarm” dense sources, where most of them are likely
formed via two-body radiative attachment, a process that is virtually unstudied both
theoretically and experimentally. With a simple phase-space theory for the process,
we and others have been able to reproduce most but not all of the observations of
molecular anions. More detailed studies of radiative attachment are clearly
required. Finally, the ortho-to-para ratio of assorted gas-phase species in the
interstellar medium is often difficult to understand. Here we consider the case of
the water cation, H2O+, where the measured ortho-to-para ratio in diffuse clouds
along the line of sight toward our galactic center is 4.8. The various processes
involved in determining this ratio are explored.
ABSTRACTS
20
Theoretical Methods for Treating Stable Anions for Which the Excess Electron Does Not Bind in the
Hartree-Fock Approximation
K. D. Jordan and V. Voora
Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260
Molecular anions can exist either as bound states (energy of the anion below
that of the ground state of the neutral) or as resonances (metastable states
embedded in the electron scattering continuum). One of the challenges to theory is
the characterization of those stable anions which, although bound, fail to bind in the
Hartree-Fock approximation. As a consequence, traditional quantum chemistry
methods such as MP2 and CCSD(T) are not applicable to these systems. We examine
two systems of this nature, water clusters with cavity-bound anions and C60, which
possesses a polarization bound s-type anion state. For the model water clusters, we
find that the ADC(2), EOM-MP2, and EOM-CCSD many-body methods all give similar
electron-binding energies. We also show that the orbital-optimized MP2 (OO-MP2)
method succeeds in binding the excess electron in these systems which
demonstrates that it is the orbital relaxation in response to low-order correlation
effects rather than high-order correlation effects that is the key to the electron
binding. We then turn our attention to C60 where we use the EOM-MP2 and EOM-
CCSD methods to demonstrate that it has an s-type polarization bound anion, with
about 10% of the electron density inside the cage and 90% outside.
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21
Analytic Three-Channel Model for Resonance-Averaged Direct and Indirect Dissociative
Recombination Processes of Molecular Ions
I. F. Schneider1, N. Pop2, and Ch. Jungen3
1 Laboratoire Ondes et Milieux Complexes UMR-6294 CNRS et Université du Havre, 25, rue Philippe Lebon, BP 540, 76058, Le Havre, France
2 Department of Physical Foundations of Engineering Polytechnical University of Timisoara RO-300223, Timisoara, Romania
3 Laboratoire Aimé Cotton du CNRS, Bâtiment 505 Université de Paris-Sud, F-91405 Orsay, France
An analytic three-channel model is developed for the description of
simultaneous direct and indirect dissociative recombination (DR) cross sections of
molecular ions with electrons. The model is for- mulated in terms of three
parameters describing the interactions between the electron-ion entrance channel,
e, the dissociation channel, d, and an `active' quasibound molecular Rydberg
channel, a, and yields resonance-averaged cross sections for low incident electron
energies. The relative magnitudes of the parameters determine (i) the height of the
downward steps at the ion vibrational thresholds and (ii) the relative contributions
of the direct and indirect processes. The model is intended to serve for the empirical
analysis of observed DR cross sections, and in particular it allows the assessment of
the extent to which re-ionization of the capture complex competes with dissociation.
The model is applied to the DR of H+3. and HCO+.
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22
Radiative Electron Attachment to Molecules of
Astrophysical Interest. Benchmark Study of CN-
Kokoouline1, N. Douguet2, S. Fonseca dos Santos2, O. Dulieu3, M. Raoult3, A. E. Orel2
1Department of Physics, University of Central Florida, Orlando, Florida 32816
2Department of CHMS, University of California at Davis, Davis, CA 95616 3Laboratoire Aime Cotton, CNRS, Bat 505, Universite Paris 11, 91405 Orsay Cedex, France
We have developed a first-principles approach to study the process of
radiative electron attachment (REA) to linea molecules of astrophysical interest Mol
+e_→ Mol-+ ħ . (Mol - = CnH- -, CnN- ). The approach is based on accurate ab initio
calculations of electronic bound and continuum states of the negative ion. The
electronic continuum states are obtained with the complex-Kohn variational
method. The benchmark calculation for the formation of the simplest observed ion,
CN-, by REA has produced a low rate coefficient, 5x10 _17 cm3/s at 30 K. We will
present also a preliminary result for the C4H- formation by REA. For this molecule,
the REA rate coefficient is expected to be larger by about a factor of 10 due to a
larger transition dipole moment. This study suggests that the negative molecular
ions, recently observed in the interstellar medium, can hardly be formed by the
process of radiative electron attachment.
The figure to the left shows potential
energy curves of the only electronic state
of CN- and several electronic states of CN.
The shape of the curves of the CN and
CN- ground states is almost the same.
The transition dipole moments are
almost geometryindependent. Thus,
during the REA process, the vibrational
quantum number is approximately
conserved.
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23
The figure to the left shows the
transition dipole moments between the
electronic bound state of CN-- and partial-
wave components of the initial CN+e-
states (continuum states). The transition
dipole moments are calculated for the
CN-equilibrium distance, R=2.27ao
The figure to the left shows the REA rate coefficients for the process starting with the ground vibrational level and different initial rotational states j (j=0,1,2,3,15) of CN. For each initial rotational state, the resulting cross-section is summed over all possible final rovibrational states of CN- .
This work is supported by the DOE Office of Basic Energy Science and the National
Science Foundation, Grant No's PHY-08-55092 and PHY-08-55622.
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24
Dissociative Recombination Measurements at Ion Storage Rings: Achievements and Perspectives
Holger Kreckel
Max-Planck-Institute for Nuclear Physics (MPIK), Heidelberg, Germany
In the past two decades heavy-ion storage rings have become the work
horses for electron recombination measurements with atomic and molecular ions.
Modern storage ring facilities provide a clean, almost background-free experimental
test bench and in combination with a collinear cold electron beam device, they allow
for precise energy-resolved recombination rate coefficient measurements with
superior resolution.
For atomic ions, the recombination is often dominated by a resonant
process, where the free electron is captured into a discrete state, while exciting one
of the bound electrons (di-electronic recombination). For molecular ions, on the
other hand, the energy gain of the capture process can be transferred into internal
energy of the neutral molecule. This can either lead to a direct non-resonant
recombination into a dissociative state (direct dissociative recombination) or
proceed through intermediate states that eventually couple to a dissociative channel
(indirect dissociative recombination).
We will give some examples that demonstrate the potential of the storage
ring technique and then focus on the dissociative recombination of the triatomic
hydrogen ion H3+. Being the simplest polyatomic molecule and a key species in the
interstellar medium, H3+ has received a lot of attention and the DR rate coefficient of
H3+ has been a controversial topic for years. We will describe the recent efforts for a
detailed comparison between measurement and theory for this benchmark
molecular ion.
Finally, we will give a brief outlook outlining the potential for DR
measurements at the new Cryogenic Storage Ring (CSR) that is currently under
development at MPIK.
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25
Complex-Scaled Equation-of-Motion Coupled-Cluster Method with Single and Double
Substitutions for Autoionizing Excited States: Theory, Implementation, and Examples
Anna Krylov
Dept. of Chemistry, University of Southern California Los Angeles, CA 90089-0482
Theory and implementation of complex-scaled variant of equation-of-
motion coupled-cluster method for excitation energies with single and double
substitutions (EOM-EE-CCSD) will be presented. The complex-scaling formalism
extends the EOM- EE-CCSD model to resonance states, i.e., excited states that are
metastable with respect to electron ejection. The method is applied to Feshbach
resonances in two well-studied systems, He and H-, The dependence of the results
on one-electron basis set is quantified and analyzed. Energy decomposition and
wave function analysis reveals that the origin of the dependence is in electron
correlation, which is essential for the lifetime of Feshbach resonances. It is found
that one electron basis should be sufficiently flexible to describe radial and angular
electron correlation in a balanced fashion and at different values of the scaling
parameter, θ. Standard basis sets that are optimized for not-complex-scaled
calculations (θ=0) are not sufficiently flexible to describe the θ-dependence of the
wave functions even when heavily augmented by additional sets.
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26
Photoionization in the Molecular Frame
Robert R. Lucchese
Department of Chemistry, Texas A&M University College Station, TX 77843
There has been a resurgence of interest in molecular photoionization and
the corresponding electron-molecular ion scattering dynamics. This interest is in
large part prompted by the development of improved and new light sources which
enable the scattering dynamics to be probed in the molecular frame. A discussion
will be given of recent studies on single photon molecular frame photoelectron
angular distributions (MFPADs) and the related recoil-frame photoelectron angular
distributions (RFPADs), multiphoton RFPADs, high harmonic generation from
impulsively aligned molecules, photoionization of impulsively aligned molecules,
and rescattering spectroscopy. In each case, an understanding of the electron-
molecular ion scattering dynamics is an essential ingredient to understanding the
whole process.
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27
Molecular Anions in the Laboratory and in Space
Michael C. McCarthy
Harvard Smithsonian Center for Astrophysics, Cambridge, USA
The importance of negative ions (anions) in astronomy was demonstrated in
1939 by Rupert Wildt who showed that H¯ is the major source of optical opacity in
the solar atmosphere, and therefore the material which one mainly sees when
looking at the sun and similar stars. Despite the detection of many neutral and
positively-charged molecules in space in the intervening 70 years, it was not until
2007 that a molecular anion (C6H¯) was identified for the first time in two rich
astronomical sources on the basis of laboratory measurements of its rotational
spectrum. Since that initial discovery, the closely-related carbon-chain anions, CCH¯,
C4H¯, C8H¯, NCO¯, CN¯, and C3N¯ were subsequently detected in our laboratory; all but
two of them have now been detected in space, and there is strong evidence for C5N¯
there as well, even thought its rotational spectrum has not yet been measured in the
laboratory. The most readily observed anion, C6H¯, has now been detected in at
least six other astronomical sources, suggesting that anions are probably widely
distributed in the interstellar gas, often present at the level of at least of few percent
relative to the neutral parent. The high abundance of CN¯ relative to CN in the
circumstellar shell of the evolved carbon star IRC+10216, and the unexpected
spatial distribution of C6H¯ relative to C6H in this source suggest that formation
routes other than radiative electron attachment may be important.
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28
Low-Energy Electron-Molecule Collisions with the Schwinger Multichannel Method†
Vincent McKoy
California Institute of Technology Pasadena, California 91125
Collisions of low--‐energy electrons with polyatomic molecules are
important in many contexts, from the astrophysical to the biological. Modelers need
cross sections for a variety of processes, among them elastic scattering, dissociative
attachment, and vibrational and electronic excitation. However, both measurements
and calculations are difficult, and data remain scarce for even the most important
molecules, such as water. In this talk, I will review the formulation we have
developed for ab initio computation of electron--‐molecule collision cross sections,
describe its numerical implementation, and discuss features of the method that are
particularly advantageous for applications to general polyatomics, as well as the
method’s limitations. Recent applications to problems such as resonant collisions
with the constituents of DNA and electronic excitation of water illustrate the
method’s capabilities. In closing, I will comment on the challenges that remain and
the prospects for addressing them.
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29
Very Low-Energy Electron-Induced Damage of DNA
Thomas M. Orlando
School of Chemistry and Biochemistry and School of Physics Georgia Institute of Technology Atlanta, GA USA 30318
We have examined theoretically and experimentally the low energy (1-25
eV) electron-induced damage of DNA oligomers. Specifically, we have calculated the
elastic scattering of 5-30 eV electrons within the B-DNA 5'-CCGGCGCCGG-3' and A-
DNA 5'-CGCGAATTCGCG-3' sequences using the separable representation of a free-
space electron propagator and a curved wave multiple scattering formalism. The
disorder brought about by the surrounding water and helical base stacking leads to
featureless amplitude build-up of elastically scattered electrons on the sugars and
phosphate groups for all energies between 5-30 eV. However, some constructive
interference features arising from diffraction were revealed when examining the
structural waters within the major groove. These appear at 5-10, 12-18 and 22-28
eV for the B-DNA target and at 7-11, 12-18 and 18-25 eV for the A-DNA target.
Though the diffraction depends upon the base-pair sequence, the energy dependent
elastic scattering features are primarily associated with the structural water
molecules localized within 8-10 Å spheres surrounding the bases and/or the sugar-
phosphate backbone. The electron density build-up occurs in regions of electron
attachment resonances, direct electronic excitation and dissociative ionization. We
correlated these scattering features with our measured DNA single and double
strand breaks and suggested that states involving major groove waters may be
important in low-energy electron induced damage of DNA. Compound resonance
states involving interfacial water and excitation energies > 5 eV seem to be required
for lethal double strand breaks.
We have also recently extended this work to excitation energies below 5 eV
by examining the damage using Raman-microscopy and scanning electrostatic force
microscopy. Very efficient damage via single strand breaks is observed below 5 eV
excitation energies. This involves π* negative ion resonances that are initially
ABSTRACTS
30
localized on the bases but transferred to the σ* states of the sugar-phosphate bond.
The efficacies of these channels depend upon the base-pair sequences as well as the
presence of water.
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31
The Dynamics of Resonant Electron Collisions with Carbon Dioxide
T. N. Rescigno
Lawrence Berkeley National Laboratory
Despite the fact that the principal features of low-energy electron-CO2
collisions have been known and studied for over forty years, there are numerous
misconceptions and significant gaps in the extant literature on the subject. The
scattering is characterized by a rapid rise in the total cross section below 1 eV,
anomalous threshold behavior for excitation of symmetric stretch and bending
vibrational modes, resonant vibrational excitation near 4 eV with weak
``boomerang'' structure in the excitation cross sections and dissociative electron
attachment cross sections leading to ground-state CO + O- which peak near 4 eV and
8 eV and have angular distributions which show large deviations from axial recoil.
The nuclear dynamics associated with all these features is intrinsically polyatomic
in nature and cannot be described with one-dimensional models. The goal of our
current work is to provide a consistent description of all these phenomena and to
resolve a number long-standing paradoxes concerning the dissociation dynamics.
ABSTRACTS
32
Complex Generalized Hartree-Fock
Eric J. Sundstrom1, David Small1, and Martin Head-Gordon1,2
1Department of Chemistry, University of California, Berkeley, California 94720
2Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720
Since the early days of quantum chemistry there has been a great deal of
discussion regarding symmetry breaking of Hartree-Fock (mean-field) wave
functions including a full group theoretical classification of these solutions.[1]
Despite the considerable discourse on this topic, due to computational concerns,
many of these broken symmetry methods (other than simple unrestriction) were
never thoroughly studied within the quantum chemistry community. Recently,
completely broken symmetry wave functions have come back into vogue and there
are many groups working with methods related to these wave functions.[2]
Here we present a fundamental study assessing for which classes of
molecular systems utilizing generalized spin and complex broken symmetry wave
functions may provide more accurate potential energy surfaces. We calculate the
eigenvalues of the Hessian which when negative indicate instability of these wave
functions; this allows us to identify saddle points and locate legitimate local minima.
Exploiting the blocked nature of the Hessian allows us to resolve internal
(symmetry retaining) and external (symmetry breaking) degrees of freedom.[3] We
also compute various spin observables to ascertain the equivalence of these solution
which may become important when using the wave functions with correlation
methods.
REFERENCES [1] HIDEO FUKUTOME, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY 20(5), PP. 955–
1065 (1981). [2] GUSTAVO E SCUSERIA, CARLOS A JIMÉNEZ-HOYOS, THOMAS M HENDERSON, KOUSIK
SAMANTA, AND JASON K ELLIS, THE JOURNAL OF CHEMICAL PHYSICS 135(12), PP. 124108 (2011). [3] ROLF SEEGER AND JOHN A POPLE, THE JOURNAL OF CHEMICAL PHYSICS 66(7), PP.3045–3050
(1977).
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33
R-matrix and Vibrational Frame Transformation in Studies of Molecular Photodetachment
Michal Tarana1, 2 and Chris H. Greene1
1Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907-2036, USA
2JILA, University of Colorado, Boulder, Colorado 80309-0440, USA
The state of the art in the theoretical treatment of the electron interactions with
small molecules can be topically divided into the ab initio scattering calculations in the fixed-
nuclei approximation based on the methods of quantum chemistry and the scattering
calculations that incorporate nuclear dynamics. Both types of methods have their own set of
issues and are subject of the theoretical research. As to the first subject, the ab initio
molecular R-matrix is a well developed tool that uses molecular electronic structure theory
for calculations of the elastic and electronically inelastic scattering matrices [1]. First, several
aspects of the ab initio R-matrix method will be discussed. The study of the 2Πg continuum
and bound states of O2- in the fixed-nuclei approximation will be presented. Various models
of neutral O2 will be introduced and the question, how well the polarization and correlation
effects can be represented using rather limiting CAS CI approach, will be addressed. An
alternative method of calculation of the R-matrix from the Hamiltonian in the inner region
will be introduced and the test of its numerical performance will be presented. This method
is designed to handle large CAS models, where the usual complete diagonalization of the
Hamiltonian becomes numerically too demanding. It is based on solving the system of linear
equations individually for every scattering energy. The energy-dependent vibrational frame
transformation (VFT) will be discussed as a theoretical tool to study the vibrational
dynamics of the electron collisions with small neutral molecules and photodetachment of
molecular anions [2, 3]. The VFT study of the photodetachment of O2- will be presented in
terms of the photoelectron angular distributions calculated for different vibrational states.
Connection between the ab initio R-matrix calculations and the VFT will be discussed. This
work was supported in part by the Department of Energy, Office of Science.
REFERENCES [1] J. TENNYSON, PHYS. REP. 491, 29 (2010). [2] H. GAO AND C. H. GREENE, J. CHEM. PHYS. 91, 3988 (1989). [3] H. GAO AND C. H. GREENE, PHYS. REV. A 42, 6946 (1990).
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Bound and Continuum States in Electron – Molecule Collisions Using the R-Matrix Method
Jonathan Tennyson
Physics & Astronomy, University College London, London WC1E 6BT, UK
Use of the R-matrix method to treat the electron-molecule collision problem
has recently been reviewed [1]. Recent work has focused on improving the
description and range of validity of the scattering problem by the use of
pseudostates, detailed calculations of bound and continuum states with a focus on
the avoided crossings and making the UK Molecular R-matrix code widely accessible
to non-experts [2]. This last task has particular importance for providing data for
models of technological plasmas and has led to the implementation of a number of
new procedures to aid this work.
The R-matrix with pseudostates method (RMPS) has been widely used in
atomic physics to extend collision calculations to the energies above the target
ionisation threshold [3]. The molecular RMPS method was originally developed to
allow for the ab initio treatment of electron impact ionisation [4]. However the
ability of the RMPS method to give a converged representation of polarisation [5]
has meant that it has become the method of choice for treating problems where
polarisation effects are important.
RMPS studies of electron collisions with C__2 anions showed that the observed
di anionic resonances are due to strong polarisation effects which overcome the
Coulomb repulsion between the two extra electrons [7]. The method was also able
to recover the background electron-impact detachment cross section due to high
impact parameter collisions which could be represented by high-ℓ transitions to
pseudo-states using the dipole Born approximation. This method has also been
successfully applied to positron –molecule collisions [8]
The RMPS method is computationally expensive and has driven the
development of algorithms which obviate the need to explicitly obtain all the
ABSTRACTS
35
eigenvectors of the inner region Hamiltonian [9]. The largest calculation attempted
so far obtaining 5000 eigenvalues for a 650 000 dimensional matrix [8]. Work on
improved parallel procedures to further extend the scope of RMPS calculations is in
progress. Electron collision calculations are important for characterizing resonances
which, for molecular ions, occur in infinite series. Such calculations can be extended
to negative scattering energies giving results also on infinite bound-state Rydberg
series and, which is of particular importance for studies of dissociative
recombination, how these states interact with dissociative resonance states Results
of a detailed study on the nitrogen molecule will be presented.
REFERENCES 1. J. TENNYSON 2010 PHYS. REP. 491 29 2. J. TENNYSON ET AL 2007 J. PHYS. CONF. SERIES, 86, 012001 3. K BARTSCHAT 1998 COMPUT. PHYS. COMM. 114 168 4. J.D. GORFINKIEL AND J. TENNYSON 2004 J. PHYS. B: AT. MOL. OPT. PHYS. 37 L343; 2005 IBI
38 1607 5. M JONES AND J. TENNYSON 2010 J. PHYS. B: AT. MOL. OPT. PHYS. 43 045101 6. G. HALMOVA AND J. TENNYSON 2008 PHYS. REV. LETT. 100 213202 G. HALMOVA ET AL 2008 J.
PHYS. B: AT. MOL. OPT. PHYS. 41 155201 7. R. ZHANG ET AL 2011 J. PHYS. B: AT. MOL. OPT. PHYS. 44 035203; IBID 44, 195203 (2011). 8. J. TENNYSON 2005 J. PHYS. B: AT. MOL. OPT. PHYS. 37 1061
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36
DESIREE: A Unique Cryogenic Electrostatic Storage Ring for Merged Ion-Beams Studies
R. D. Thomas
Department of Physics, Stockholm University, SE-106 91 Stockholm, Sweden
In this presentation I will describe the design and construction of a novel
type of ion storage device currently undergoing commissioning at Stockholm
University, Sweden. This device uses purely electrostatic focusing and deflection
elements and allows ion beams of opposite charge to be confined under extreme
high vacuum and cryogenic conditions in separate “rings” and then merged over a
common straight section. The unique construction of this Double ElectroStatic Ion
Ring ExpEriment (DESIREE) apparatus allows for studies of interactions between
cations and anions at low and well-defined centre-of-mass energies down to 10 meV
as was achieved in magnetic storage rings between ions and electrons (see e.g. ref.
1). The heart of DESIREE is shown schematically in Fig. 1.
Figure 1: A schematic of DESIREE’s heart: the cooled rings and merging region.
ABSTRACTS
37
The technical advantages of using purely electrostatic over magnetic
elements are many, but the most relevant are: electrostatic elements are more
compact and easier to construct; remanent fields, hysteresis and eddy-currents,
highly problematic in magnetic devices, are no longer relevant, and for low energy
ion beams (keV vs MeV) electrostatic elements are more efficient to use. I will
present the current state of the DESIREE facility: the system is now under vacuum at
cryogenic temperatures & results from the first injection show storage of low
energy ions up to 30 minutes, and highlight some of the technical issues that have
arisen during its development and construction [2].
Finally, the advantages of this design are a boon to fundamental
experimental studies, not only in atomic and molecular physics but also in the
boundaries of these fields with chemistry and biology, and I will finish by discussing
several examples of such potential research.
REFERENCES [1] R. D. THOMAS, MASS SPECTROM. REV., 77, 485 (2008) [1] R. D. THOMAS ET AL., REV. SCI. INSTRUM. 82, 065112 (2011)
DIRECTIONS
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