Transcript Slide 1

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 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Dissociative recombination of molecular ions
Neutral fragments
Molecular ion
AB+ + eFree electron
A+B
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Brief History of Dissociative Recombination (DR)
Solar radiation produces a lot of electrons in the Ionosphere by photoionization.
How are these electrons removed?
O2+ + e- → O* + O
1st step: DR of O2+
O (1S → 1D) emission at 5577 Å
2nd step: emission from excited atomic products
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Dissociative recombination of molecular ions
Direct DR process
Bates, D.R., “Dissociative Recombination”, Phys. Rev. 78, 492 (1950)
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Importance of DR in the interstellar medium
H3+ formation
H2
and destruction
Water formation
Carbon chemistry
O
H3+
C+
cosmic ray
OH+
OH
H2
+
H2
CO+
H2
H3
OH2+
H2
+
e-
H2 + H
H+H+H
H2
HCO+
OH3+
e-
e-
OH + H2
H2O + H
H + CO
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
The Problem with H3+ DR (experiment)
H2+H
H+H+H
DR rate coefficient
H3
++e-
upper limits
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
The Problem with H3+ DR (experiment)
H2+H
H+H+H
DR rate coefficient
H3
++e-
upper limits
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Storage ring measurements: concept
Advantages
• radiative relaxation
of internal excitations
(rotation, vibration)
• direct measurement
• 100% detection efficiency
• high resolution
Problem
H 3+
• Vibrations cool
• Rotations stay forever
Kreckel et al., PRA A 66, 052509 (2002),
Kreckel et al., New J. Phys. 6, 151 (2004)
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Rotationally “cold” ion sources
Gas inlet
2 atm
H2
5 cm
Solenoid
valve
Pinhole
flange/ground
electrode
-900 V
ring
electrode
CRYRING
2002
Supersonic
expansion
H3+
Cryogenic
ion trap
TSR
2004
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Storage ring results with “cold” H3+ ion sources
● TSR electron temp.
kT┴=0.5 meV ~ 6K
kT||=25 μeV
trap temp. 13 K
Kreckel, PRL 95, 263201 (2005)
● CRYRING
Theory
Kokoouline
and Greene
kT┴= 2 meV
ion temp. 30-50 K
McCall, Nature
422, 500 (2003)
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
The holy grail: state specific measurements
+
H3+
rotational
levels
ortho
I = 3/2
+
para
I = 1/2
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Nuclear spin effect: exp. and theory 2005
۰para H2
experiment
۰normal H2 kT┴=4 meV
theory
Greene et al.
- para
- ortho
Kreckel et. al, PRL 95, 263201 (2005)
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Theory with more accurate resonance energies
S. Fonseca dos Santos et al., JCP 127, 124309 2007
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Piezo expansion source
plunger
locking nut
discharge
electrode
skimmer
high pressure
H2 reservoir
low pressure
pinhole
6 cm
piezo actuator
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Rotational temperature of H3+ inferred from
cavity ring-down spectroscopy of the ion source
pure H2 discharge, 2bar
Trot=110 K
1:5 H2:Argon discharge, 2bar
Trot=180 K
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Nuclear spin manipulation
ortho H3+
1:5 n-H2 : Argon mixture
1:5 p-H2 : Argon mixture
para H3+
para H3+
p-H3+ fraction p3= (47.9 ± 2) %
p-H3+ fraction p3= (70.8 ± 2) %
DR 2010, Lake Tahoe, Aug19th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
DR measurements at TSR
UI Champaign-Urbana
MPI-K Heidelberg
Test Storage Ring
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Comparison to CRYRING 2002
TSR 2009 (n-H2:Ar 1:5)
CRYRING 2002 (n-H2)
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
2-dimensional imaging of the 3-body breakup
ne(cooler) = 1.4 x 107 cm-3
ne(target) = 1.34 x 106 cm-3
H3+ + e-
H+H+H
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
2-dimensional imaging of the 3-body breakup
H3+ + erotational
temperatures
(uncertainties ~ 200 K)
950 K
450 K
200 K
H+H+H
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Conditions on-axis downstream of the nozzle
skimmer
Collisional
heating during
Ion extraction?
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Nuclear spin dependence of the rate coefficient
Reduced
rate coeff.
1:5 n-H2 : Argon mixture
1:5 p-H2 : Argon mixture
Extrapolation:
100% ortho H3+
100% para H3+
p3= (47.9 ± 2) %
p3= (70.8 ± 2) %
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: 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.
Results: Kreckel et al., 82, 042715 (2010)
Petrignani et al., in preparation
The holy grail?
Still out there …
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Collaboration
TSR
Group
University
of Illinois
Kyle N. Crabtree
Brian A. Tom
Benjamin J. McCall
Oldřich Novotny*
Annemieke Petrignani
Max H. Berg
Dennis Bing
Manfred Grieser
Claude Krantz
Michael Lestinsky*
Mario B. Mendes
Christian Nordhorn
Roland Repnow
Julia Stützel
Andreas Wolf
Weizmann
Institute
Henrik Buhr
Stockholm
University
Richard Thomas
*Columbia University, NY
Funding:
National
Science
Foundation
Max-Planck
Society
German-Israeli
Foundation
Eurppean
Comission
MWAM 2010, Nov6th 2010
Holger Kreckel
Storage ring measurements … of H3+: a closer look
Perspectives:
the case to continue the quest
It is crucial to understand:
H3+ + H2 and
H3+ (J=1,K=0,1) + e-
Next speaker: Kyle Crabtree