IV In‐House Symposium  

on  

Atomic and Molecular Physics 

January 11, 2009 

Department of Physics, IIT Madras, Chennai 600 036 

 

 

 

Abstracts

Program 

Venue: Seminar Room (HSB 209), Department of Physics, IIT Madras 

 

09.30 – 09.35    Welcome Speech by P. C. Deshmukh 

09.35 – 09.40    Inaugural Address by S. T. Manson  

SESSION I    Chair Person: Ummal Momeen 

09.40 – 10.10    Karan Govil 

Relativistic and confinement effects in E1 and E1‐E2 photoionization of Xe 

10.10 – 10.40    A. J. Siji 

Effect  of  spin‐orbit  interaction  activated  interchannel  coupling  in  E1 photoionization from 4d subshell of @Xe 

10.40 – 11.10    Vivishek Sudheer 

Scattering of electrons off hollow cylindrical potential 

11.10 – 11.30    Tea Break 

 

SESSION II    Chair Person: S. Sunil Kumar 

11.30 – 12.00    Jobin Jose 

Photodetachment of Cl−:   E1 and E2 photoelectron angular distributions near Cooper minima 

12.00 – 12.30    Gagan Bihari Pradhan 

Relaxation effects on the photoionization of inner shells of atoms and ions of Mg and Ar isonuclear sequence 

 

12.30 – 14.00    Lunch Break 

 

 

SESSION III    Chair Person: Gagan Bihari Pradhan 

14.00 – 14.30    S. Sunil Kumar 

Breakup  of  the  SF63+  photoion  revealed  by  momentum  correlation 

between fragments 

14.30 – 15.00    Ummal Momeen 

Spectroscopic study of Zeeman and magneto‐optic effect in Rb atoms 

15.00 – 15.20    Tea Break 

 

SESSION IV    Chair Person: Jobin Jose 

15.20 – 15.50    Alak Banik 

Rubidium Atomic Clock 

15.50 – 16.20    Umesh Kadhane 

Near–infrared Photoabsorption by C60 Dianions in a Storage Ring 

16.20 – 16.25    Concluding Remarks by Vojislav Radojević

16.25 – 16.30    Vote of Thanks by P. C. Deshmukh

 

 

Each talk will consist of 25 minutes, and 5 minutes will be provided for Questions/Answers 

 

 

Relativistic and confinement effects in E1 and E1-E2

photoionization of Xe

Karan Govil∗, P. C. Deshmukh and A. J. Siji

Department of Physics, Indian Institute of Technology Madras, Chennai 600036

The effect of spin-orbit interaction activated interchannel coupling (SOIAIC) in 4d dipole pho-toionization channels of Xe on the 5s photoionization amplitudes is studied and analyzed. Thedramatic effect of confinement of the Xe atom in a C60 cage on the 4d photoionization parametersand the consequent effect on 5s photoionization via interchannel coupling is also discussed. Thecalculation of photoionization parameters is carried out in Relativistic Random Phase Approxima-tion [1] (RRPA) framework at different levels of truncation. Due to the cascading of SOIAIC effectin 4d photoionization to 5s photoionization mediated by interchannel coupling, new relativisticcorrelation confinement resonances [2] are observed.

A further study of E1-E2 photoionization in the energy range (12-220 eV) by including the 4pphotoionization channels confirms the presence of a new confinement resonance and modificationof SOIAIC effect in Xe 4p photoionization reported earlier in [3] for the photoionization of free Xe.The RRPA calculations for E1-E2 photoionization are performed by coupling the channels from 4s,4p, 4d, 5s and 5p subshells. Similar to the case of E1 photoionization, the SOIAIC effect in 4p pho-toionization is found to affect the quadrupole cross-section and photoelectron angular distributionparameters for 4d, 5s and 5p subshells. A new confinement and correlation confinement resonanceis observed at about 185 eV in 4p, 4d, 5s and 5p photoionization. These confinement resonancesalso affect the photoelectron angular distribution for E1-E2 photoionization.

References:

1. Johnson et al., Phys. Rev. A 20 964 (1979)

2. Dolmatov et al., J. Phys. B: At. Mol. Opt. Phys. 41 165001 (2008)

3. Sunil Kumar et al., DAMOP, Pennsylvania, USA, May 27-31 (2008)

∗E-mail of correspondence: karangovil@gmail.com

Effect of spin-orbit interaction activated interchannel

coupling in E1 photoionization from 4d subshell of @Xe

A. J. Siji∗, Karan Govil and P. C. Deshmukh

Department of Physics, Indian Institute of Technology Madras, Chennai 600036

Photoionization of atoms trapped in a C60 fullerene cage has received much attraction in re-cent years. The modification of well known spin orbit interaction activated interchannel coupling(SOIAIC) [1] due to the presence of confinement was recently reported in [2]. In the present study,a detailed study of the absolute value of matrix elements for the dipole photoionization of freeand confined Xe is performed. The calculations were performed in Relativistic Random PhaseApproximation (RRPA) [3] framework by coupling the photoionization channels from 4d, 5s and5p subshells. The matrix elements provide a detailed understanding of the SOIAIC effect and theconfinement resonances. The rate of change of photoionization cross-section is also studied whichshows that the weaker photoionization channels are the ones which are affected more as expected.

References:

1. Amusia et al., Phys. Rev. Lett. 88 093002 (2002)

2. Karan et al., J. Phys. B: At. Mol. Opt. Phys. (Communicated, Dec 2008)

3. Johnson et al., Phys. Rev. A 20 964 (1979)

∗E-mail of correspondence: sijialappattu@gmail.com

Scattering of Electrons off Hollow Cylindrical Potentials

Vivishek Sudhir*, Pranawa Deshmukh

Department of Physics, Indian Institute of Technology Madras, Chennai, India 600 036

* E-mail of correspondence: vivishek.sudhir@gmail.com

We study the scattering of electrons off a hollow cylindrical potential. Longitudinal

incidence (along the cylinder’s axis) has been studied in literature [1,2], but to the best of our

knowledge, there is no work reported for the case of transverse incidence, except in the case of a

delta-function potential [3]. In this work, we have considered scattering of a beam of electrons

that is incident along the transverse direction relative to the cylinder. Solutions in closed forms

are obtained for the case when the incident beam is a plane wave. It is demonstrated that in the

limiting case in which the cylindrical potential approaches the delta-function potential, the

results agree with those in literature [3]. The scattering cross-section that appears as an infinite

sum over partial waves corresponding to different

azimuthal quantum number is shown to converge

rapidly so that for all practical applications only the

first few terms would suffice. Angular distribution of

the scattered flux is also studied. It is found that at

certain specific energies that correspond to the bound

states of the cylindrical potential, the scattering cross-

section vanishes (Figure 1). Figure 1. Partial Cross Sections for U=50; m=0 (red), m=1 (blue), m=2 (black) and m=3 (green).

References:

1. M. Olshanii, ‘Atomic Scattering in the Presence of an External Confinement and a Gas of Impenetrable Bosons’, Phys. Rev. Lett. 81 5 (1998)

2. J. I. Kim, J. Schmiedmayer, P. Schmelcher, ‘Quantum scattering in quasi-one-dimensional cylindrical confinement’, Phys. Rev. A 72 042711 (2005)

3. L. I. Schiff, ‘Quantum Mechanics’, Mc Graw Hill Publications (1968)

Photodetachment of Cl−: E1, E2 photoelectron angular distribution near Cooper minima

Jobin Jose, Gagan Bihari Pradhan and P. C. Deshmukh*

Department of Physics, Indian Institute of Technology Madras, Chennai 600036

* E-mail of correspondance: pcd@physics.iitm.ac.in

Photodetachment of negative ions has attracted a lot of attention in recent investigations since it provides deep insight into the dynamics of correlations. Studies of photoionization parameters in the vicinity of the Cooper minimum is of great importance as various properties of the photoelectron attain rather specific values at the energy corresponding to it [1]. In the present work, analysis of photodetachment of the 3p and 3s electrons of Cl− has been carried out employing E1 (electric dipole) and E2 (electric quadrupole) coupling near the Cooper minima in the photodetachment channels using the relativistic random phase approximation (RRPA) [2]. The methodology adopted earlier to investigate photoionization near the E2 Cooper minimum in 5s photoionization of atomic Xenon [3] has been used. A detailed analysis of the non-dipole angular distribution asymmetry parameters confirms the presence of the quadrupole (E2) Cooper minimum.

References:

[1] Banerjee et al., Phys. Rev. A 75 042701 (2007)

[2] Johnson et al., Phys. Rev. A 20 966-977(1979)

[3] P. C. Deshmukh et al., J. Phys. B 41 021002 (2008)

Relaxation effects on the photoionization of inner shells of atoms and ions of Mg and Ar isonuclear sequences

Gagan Bihari Pradhan1, Jobin Jose1, P. C. Deshmukh1* and V.Radojevic’2

1Department of Physics, Indian Institute of Technology Madras, Chennai 600036

2Institute of Physics, Belgrade, Serbia 11080 * E-mail of correspondence: pcd@physics.iitm.ac.in

Analysis of atomic/ionic data is often done in terms of three alternative schemes: isoelectronic (N constant), isonuclear (Z constant) and isoionic (z=Z-N+1 constant). Studies of atoms/ions belonging to the isonuclear sequence are of great importance for their applications in fusion plasma, tokamaks and in astrophysics [1, 2]. In the present work, photoionization of inner shells of atoms/ions belonging to the Mg and Ar isonuclear sequences are investigated using (i) Relativistic Random Phase Approximation with Relaxation (RRPA-R) [3] and also (ii) RRPA without relaxation [4]. Comparison of results obtained using these two approximation reveal an important effect of relaxation, namely that inner-shell photoionization is always sensitive to the removal of outer electrons, contrary to what is generally believed.

References:

1. Colgan et al. Phys. Rev. A 77 062704 (2008)

2. Nasreen et al. Phys. Rev. A 40 6091 (1989)

3. Radojevic’ et al. Phys. Rev. A 40 727 (1989)

4. Johnson et al. Phys. Rev. A 20 964 (1979)

Breakup of the SF63+ Photoion Revealed by

Momentum Correlation between Fragments

S. Sunil Kumar1*, P. C. Deshmukh1, R. K. Kushawaha2, V. Sharma3, I. A. Prajapati2, K. P. Subramanian2 and B. Bapat2

1Indian Institute of Technology Madras, Chennai 600 036

2Physical Research Laboratory, Ahmedabad 380 009 3JILA, University of Colorado, Boulder, CO 80309

* E-mail of correspondence: sunilks@physics.iitm.ac.in

Fragmentation of SF63+, formed from SF6 by absorption of soft x-ray photons, has been

investigated using a momentum imaging time-of-flight spectrometer. We observe triple ion coincidences between two F+ ions and SFm

+ where m = 0 – 3. Strong correlation between the momentum distributions of the two F+ ions is observed across all dissociation channels involving triple ion coincidences. We present a method [1] of estimating the contribution of the neutral fragments to the kinematics of ion ejection based on the scalar triple product of the ion momentum vectors. The noncoplanarity of the three ion ejecta inferred in this manner allows us to discern the fragmentation sequence of SF6

3+. The proposed sequence is loss of a neutral F followed by violent ejection of two F+ ions and gentle removal of remaining F atoms from SF3

+.

Fig. 1. Momentum correlation maps between the two F+ ions in the triple ion coincidences F+:F+:SFm

+ (m = 0 – 3). The momentum of the first detected F+ ion is taken as the reference (blue arrow). The components of the momentum of the second F+ ion parallel and perpendicular to the reference vector are plotted. The color scale shows the number of events. The histogram accompanying the arrow shows the distribution of the magnitude of the momentum of the first ion.

References:

1. Sunil Kumar et al,. Phys. Rev. A 78 062706 (2008)

Spectroscopic study of Zeeman and Magneto-optic effects in Rubidium atoms

M. Ummal Momeen*, G. Rangarajan and P. C. Deshmukh

Department of Physics, Indian Institute of Technology Madras, Chennai 600 036

* E-mail of correspondence: momeen@physics.iitm.ac.in

Magneto- optical effects in rubidium atomic vapour have led to the understanding of many interesting phenomena such as the study of Hanle effect, Zeeman splitting, magneto- optical rotation (Faraday and Voigt effects) and atomic coherence properties. These effects have potential applications towards atomic magnetometer, laser frequency stabilization and quantum information processing [1-3].

The essence of this work is to control the linear and nonlinear magneto- optical effects by applying external magnetic and optical fields. Zeeman profile of rubidium atomic system has been studied to understand the influence of weak/intermediate magnetic fields on the atomic hyperfine spectrum. The non-linearity of Zeeman sublevels and optical pumping effects play a major role in the intensity variation in magnetic fields ranging from 0 to 50 G [4]. External magnetic field can induce linear [5] or non-linear magneto-optical effects by introducing frequency shifts among various Zeeman sublevels of atomic vapors. Non-linear magneto-optical rotation and optical field induced polarization rotation have also been discussed.

References:

1. Lukin et al. Nature. 413 273 (2001)

2. Budker et al. Rev. Mod. Phys. 74 1153 (2002)

3. Budker et al. Nature Physics. 3 227 (2007)

4. Momeen et al. J. Phys. B: At. Mol. Opt. Phys. 40 3163 (2007)

5. Momeen et al. J. Phys.: Conference Series 80 012033 (2007)

Rubidium Atomic Clock

Alak Banik1,2*

1Department of Physics, Indian Institute of Technology Madras, Chennai 600 036 2Space Applications Center, Ahmedabad 380 015

*E-mail of correspondence: ph09d003@smail.iitm.ac.in

Atomic clocks are basic system block for Universal Time scale, Satellite Navigation, Deep Space Communication and synchronous digital communication. With the advent of GPS system, clock developments are progressed a lot towards the availability of the commercial products in various communication areas. For time-in-space concept, satellites carry on-board atomic clocks with navigation payload which provide position and timing services to users. So, space clocks are required to be smaller in size, weight and power consumption [1, 3] with maintaining the required stability performance. The functional block schematic of conventional Lamp Pumped Rubidium Vapor Cell clock is shown in Fig.1. The microwave interrogation makes it necessary to use microwave cavity around 6.834 GHz. So, the physics package, where atomic double resonance occurs, makes the overall clock size bigger. The various internal process variations for atomic resonance and other external parameters like temperature, magnetic field variations are responsible for long and short term frequency stability of atomic clocks. Works and researches are going around the world for deterministic behaviour of various events-light shift [2], pressure shift & position shift on stability during warm up and equilibration period. Also sudden frequency jump phenomena in the clock stability are not yet well understood. Recent developments show that quite lot of works has progressed for scope of miniaturized rubidium atomic clock with better stability performance.

HEATER& TEMP. CONTROLLER

SOURCE CURRENT

LAMP RF EXCITER

LAMP

FILTER C

ELL

RESO

NA

NC

E CELL

PHO

TO D

ETCT.

C-FIELD COIL

LAMP & RES.CELL OVEN

PHYSICS PACKAGE with magnetic shield

PRE A

MPLIFIER

MICROWAVESYNTHESIZEDSOURCE

VC-OCXO

MODULATION SIGNAL

SYNCHRONOUS DETECTOR

2ND HARMONIC DETECTOR

LOGIC &PI CONTROLLER

SERVO

BUFFERAMPLIFIER

MICROWAVEBOARD

CONTROLLER&HEALTH MONITOREPC

CONDITIONER

HEATER& TEMP. CONTROLLERHEATER& TEMP. CONTROLLER

SOURCE CURRENTSOURCE CURRENT

LAMP RF EXCITERLAMP RF EXCITER

LAMP

FILTER C

ELL

RESO

NA

NC

E CELL

PHO

TO D

ETCT.

PHO

TO D

ETCT.

C-FIELD COIL

LAMP & RES.CELL OVEN

PHYSICS PACKAGE with magnetic shield

PRE A

MPLIFIER

PRE A

MPLIFIER

MICROWAVESYNTHESIZEDSOURCE

MICROWAVESYNTHESIZEDSOURCE

VC-OCXO

VC-OCXO

MODULATION SIGNALMODULATION SIGNAL

SYNCHRONOUS DETECTORSYNCHRONOUS DETECTOR

2ND HARMONIC DETECTOR2ND HARMONIC DETECTOR

LOGIC &PI CONTROLLER

LOGIC &PI CONTROLLER

SERVO

BUFFERAMPLIFIERBUFFERAMPLIFIER

MICROWAVEBOARD

CONTROLLER&HEALTH MONITOR

CONTROLLER&HEALTH MONITOREPC

CONDITIONER

Fig.1.The functional block schematic of conventional Lamp Pumped Rubidium Vapor cell clock

References:

1. Lutwak et al., Proceedings of the 36th Annual PTTI Systems and Applications Meeting, Washington DC., Dec 7-9 (2004)

2. Mileti et al., Proceedings of the 8th EFTF, March 9-11, Munich, Germany, pp. 377-384 (1994)

3. Knappe et al., Optics Express, 13 1249 (2005)

Near–infrared Photoabsorption by C60 Dianions in a Storage Ring

Umesh Kadhane*

Department of Physics, Indian Institute of Technology Madras, Chennai 600 036

*E-mail of correspondence: rkumesh@gmail.com

A detailed study is made for the electronic structure and the stability of C60 dianions in the gas phase. Monoanions have been extracted from a plasma source and converted to dianions by subsequent electron transfer in a Na vapor cell. The dianions were stored in an all electrostatic in storage ring called ELISA at Aarhus University, Denmark and their near–infrared absorption spectrum (Fig. 1) was measured by observation of laser induced electron detachment. From the time dependence of the decay after photon absorption we conclude that the detachment is a statistical process after internal conversion, and this implies that the height of the Coulomb barrier is at least ~1.5 eV. The observed spectrum corresponds to an electronic transition from a t1u LUMO of C60 to the t1g LUMO+1 level. The electronic levels of the dianion are split due to Jahn-Teller coupling to quadrupole deformations of the molecule and a main absorption band at 10726 cm−1 corresponds to a transition between the Jahn–Teller ground states. Also transitions from excited pseudo-rotational states 200 cm−1 and 420 cm−1 below this band are observed. We argue that a very broad absorption band around 12500 cm−1 consists of transitions to so called cone states, which are Jahn–Teller states on a higher potential energy surface, stabilized by a pseudo–rotational angular momentum barrier. For C60

2− ions in solution ESR measurements have indicated a singlet ground state, and from the similarity of the absorption spectra we conclude that also the ground state of isolated C60

2− ions is also a singlet. The details of the experiment will be presented in the talk.

Fig. 1. a) Absorption spectra for Ttrap ~ 300 K and laser pulse at 10.8 ms (Δ) and Ttrap ~ 100 K and laser pulse at 32 ms (•). The inset shows the peak region with fits discussed in the text. b) Absorption spectra for C60

2− ions in MTHF at 77 K and in benzonitrile at room temperature.