Storage ring measurements of the Dissociative Recombination of H 3 + : a closer look

Storage ring measurements of the Dissociative Recombination of H3

+: a closer look

Holger Kreckel University of Illinois at Urbana-Champaign

A fundamental process in space …. … studied in the laboratory.

MWAM 2010, Nov6th 2010Holger Kreckel Storage ring measurements … of H3

+: a closer look

AB+ + e- A + B

Dissociative recombination of molecular ions

Molecular ion

Free electron

Neutral fragments


+: a closer look

Brief History of Dissociative Recombination (DR)

O2+ + e- → O* + O

1st step: DR of O2+

O (1S → 1D) emission at 5577 Å 2nd step: emission from excited atomic products

Solar radiation produces a lot of electrons in the Ionosphere by photoionization.How are these electrons removed?


+: a closer look

Dissociative recombination of molecular ions

Direct DR process

Bates, D.R., “Dissociative Recombination”, Phys. Rev. 78, 492 (1950)


+: a closer look

Importance of DR in the interstellar medium

H3+ formation

and destructionH2 H2

+ H3+

cosmic ray H2H2 + H

H + H + H

e-

O H3

+

OH+ OH2+

H2OH3

+H2 e-

OH + H2

H2O + HWater formation

C+ OH

CO+H2

HCO+ e-

H + COCarbon chemistry


+: a closer look

H3

++e- H2+H

H+H+H

The Problem with H3+ DR (experiment)

upper limits

DR

rat

e co

effic

ient

Storage ring measurements: concept

• radiative relaxation of internal excitations (rotation, vibration)

• direct measurement

• 100% detection efficiency• high resolution

Advantages

Problem

H3+


+: a closer look

• Vibrations cool

• Rotations stay forever

Kreckel et al., PRA A 66, 052509 (2002),Kreckel et al., New J. Phys. 6, 151 (2004)

H2Gas inlet

2 atm

Solenoid valve

-900 Vring

electrode

Pinhole flange/ground

electrode

H3+

Rotationally “cold” ion sources

Supersonicexpansion

CRYRING 2002

5 cm

Cryogenic ion trap

TSR2004


+: a closer look

● TSR electron temp. kT┴=0.5 meV ~ 6KkT||=25 μeV trap temp. 13 KKreckel, PRL 95, 263201 (2005)

● CRYRING kT┴= 2 meVion temp. 30-50 KMcCall, Nature 422, 500 (2003)

Storage ring results with “cold” H3+ ion sources

TheoryKokooulineand Greene


+: a closer look

+

orthoI = 3/2

paraI = 1/2

+

The holy grail: state specific measurements

H3+

rotationallevels


+: a closer look

Nuclear spin effect: exp. and theory 2005

۰para H2

۰normal H2

experimentkT┴=4 meV

theoryGreene et al.

- para- ortho

Kreckel et. al, PRL 95, 263201 (2005)


+: a closer look

Theory with more accurate resonance energies

S. Fonseca dos Santos et al., JCP 127, 124309 2007


+: a closer look

skimmerdischarge electrode

pinhole

plunger

piezo actuator

locking nut

6 cm

high pressureH2 reservoir

low pressure

Piezo expansion source


+: a closer look

Rotational temperature of H3+ inferred from

cavity ring-down spectroscopy of the ion source

pure H2 discharge, 2barTrot=110 K

1:5 H2:Argon discharge, 2barTrot=180 K


+: a closer look

Nuclear spin manipulation

1:5 n-H2 : Argon mixture p-H3+ fraction p3= (47.9 ± 2) %

1:5 p-H2 : Argon mixture p-H3+ fraction p3= (70.8 ± 2) %

ortho H3+ para H3

+ para H3+


+: a closer look

DR 2010, Lake Tahoe, Aug19th 2010Holger Kreckel Storage ring measurements … of H3

+: a closer look

UI Champaign-Urbana

MPI-K Heidelberg

DR measurements at TSR

Test Storage Ring

Comparison to CRYRING 2002

CRYRING 2002 (n-H2)

TSR 2009 (n-H2:Ar 1:5)


+: a closer look

2-dimensional imaging of the 3-body breakup

H3+ + e- H + H + H

ne(cooler) = 1.4 x 107 cm-3

ne(target) = 1.34 x 106 cm-3


+: a closer look

2-dimensional imaging of the 3-body breakup

950 K450 K200 K

rotational temperatures(uncertainties ~ 200 K)

H3+ + e- H + H + H


+: a closer look

Conditions on-axis downstream of the nozzle

Collisional heating during Ion extraction?

skimmer


+: a closer look

Nuclear spin dependence of the rate coefficient

1:5 n-H2 : Argon mixture

1:5 p-H2 : Argon mixture

p3= (47.9 ± 2) %p3= (70.8 ± 2) %

Extrapolation:100% ortho H3

+

100% para H3+

Reducedrate coeff.


+: a closer look

Summary• While we measure a rotational temperature of 200K with CRD spectroscopy,the stored H3

+ ions are much hotter than the ion source.

• We observed clear differences between different ion sources→ the heating is probably happening prior to injection into the ring .

• We observed for the first time detailed structures in the rate coefficients for ortho-H3

+ and para-H3+ at low energies.

The holy grail?

Still out there …

Results: Kreckel et al., 82, 042715 (2010)Petrignani et al., in preparation


+: a closer look

Collaboration

Kyle N. CrabtreeBrian A. TomBenjamin J. McCall

Oldřich Novotny*Annemieke PetrignaniMax H. BergDennis BingManfred GrieserClaude KrantzMichael Lestinsky*Mario B. MendesChristian NordhornRoland RepnowJulia StützelAndreas Wolf

TSRGroup

Universityof Illinois

Richard Thomas

StockholmUniversity

Henrik Buhr

WeizmannInstitute

*Columbia University, NY

Funding: NationalScienceFoundation

Max-PlanckSociety

German-IsraeliFoundation

Eurppean Comission


+: a closer look

Perspectives:the case to continue the quest

Next speaker: Kyle Crabtree

It is crucial to understand:H3

+ + H2 andH3

+ (J=1,K=0,1) + e-


+: a closer look

Storage ring measurements of the Dissociative Recombination of H 3 + : a closer look

Documents

Transcript of Storage ring measurements of the Dissociative Recombination of H 3 + : a closer look