observation of nuclear spin selection rules in supersonically expanding plasmas containing h 3 +
DESCRIPTION
Observation Of Nuclear Spin Selection Rules In Supersonically Expanding Plasmas Containing H 3 +. Brian Tom, Michael Wiczer, Andrew Mills, Kyle Crabtree, and Ben McCall. Department of Chemistry. Department of Astronomy. →. +. +. +. +. Motivations. Source of para-H 3 + - PowerPoint PPT PresentationTRANSCRIPT
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Observation Of Nuclear Spin Selection Observation Of Nuclear Spin Selection Rules In Supersonically Expanding Plasmas Rules In Supersonically Expanding Plasmas
Containing HContaining H33++
Brian Tom, Michael Wiczer,Brian Tom, Michael Wiczer,Andrew Mills, Kyle Crabtree,Andrew Mills, Kyle Crabtree,
and Ben McCalland Ben McCall
Department of Chemistry Department of Astronomy
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MotivationsMotivations
• Source of para-H3+
– Dissociative recombination studies
• H3+ + H2 → H3
+ + H2
– Simplest reaction of polyatomic
• Interstellar o/p H3+
– To/p Tkin ??
+ → +++
Cygnus OB2 12
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• Produce para-H2
Para-HPara-H22 + Para-H + Para-H22+ + →→ Para-H Para-H33
++ + H + H
n-H2
p-H2
n-H2
p-H2
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Para-HPara-H22 + Para-H + Para-H22+ + →→ Para-H Para-H33
++ + H + H
• Produce para-H2
• Ionize para-H2
• React to para-H3+ + → +
+
+
+ → +e- 2e-
+
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HH33++ + H + H22 → (H→ (H55
++)* → H)* → H33++ + H + H22
“identity”
“hop”
“exchange”
H5+
1
3
6hop/exchange = 0.5
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Dynamics of ReactionDynamics of Reaction
C2v
D2dC2v
“hop”
“exchange”
Not obvious that “statistical” hop/exchange = 0.5 is valid!
~30
00 c
m-1
~50 cm-1
~1500 cm-1
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Spin-Modification ProbabilitySpin-Modification Probability
Total I o-H3+ + o-H2 o-H3
+ + p-H2 p-H3+ + o-H2 p-H3
+ + p-H2
o-H3+ + o-H2
5/2 1 1 0 0 0 0 0 0
3/2 4/9 1/36 0 5/12 5/9 5/9 0 0
1/2 1/9 1/9 0 0 8/9 2/9 0 2/3
o-H3+ + p-H2 3/2 0 5/12 0 1/4 1 1/3 0 0
p-H3+ + o-H2
3/2 5/9 5/9 1 1/3 4/9 10/9 0 0
1/2 8/9 2/9 0 0 1/9 17/18 1 5/6
p-H3+ + p-H2 1/2 0 2/3 0 0 1 5/6 1 1/2
Rea
ctan
ts
Products formed by Hop and Exchange
Park & Light JCP 126, 044305 (2007)
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Spin-Modification ProbabilitySpin-Modification Probability
Total I o-H3+ + o-H2 o-H3
+ + p-H2 p-H3+ + o-H2 p-H3
+ + p-H2
o-H3+ + o-H2
5/2 1 1 0 0 0 0 0 0
3/2 4/9 1/36 0 5/12 5/9 5/9 0 0
1/2 1/9 1/9 0 0 8/9 2/9 0 2/3
o-H3+ + p-H2 3/2 0 5/12 0 1/4 1 1/3 0 0
p-H3+ + o-H2
3/2 5/9 5/9 1 1/3 4/9 10/9 0 0
1/2 8/9 2/9 0 0 1/9 17/18 1 5/6
p-H3+ + p-H2 1/2 0 2/3 0 0 1 5/6 1 1/2
Rea
ctan
ts
Products formed by Hop and Exchange
1/2 0 ↔ 3/2 0 1/2 0 ↔ 3/2 1Park & Light JCP 126, 044305 (2007)
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Low Temperature EffectsLow Temperature Effects
• In pure p-H2
– p-H3+ → o-H3
+ requires p-H2 → o-H2
orthoI = 3/2
paraI = 1/2
paraI = 0
orthoI = 1
170 K
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Oka Group ExperimentsOka Group Experiments
o-H3+ p-H3
+
Pulsed Hollow CathodePositive Column Cell
Cordonnier et al. JCP 113, 3181 (2000)
p-H2→o-H2
hopexch ~2.4
@ 400 K
[not 0.5!]
p-H2
n-H2
o-H3+
p-H3+
n-H2 p-H2
reaction not yetmeasured at low T
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Supersonic Expansion Ion SourceSupersonic Expansion Ion Source
• Developed for DR experiments
• H3+ formed near nozzle
• [p-H2]/[H2] “frozen”• [p-H3
+]/[H3+] evolves, but
~ steady state• Probed by spectroscopy
H2Gas inlet
2 atm
Solenoid valve
-450 Vring
electrode
Pinhole flange/ground
electrode
H3+
McCall et al. PRA 70, 052716 (2004)
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2.8 – 4.8 2.8 – 4.8 m DFG Systemm DFG System
Ti:Sapph700 – 990 nm
532 nmpump laser
reference cavity
dichroic
/2
Nd:YAG1064 nm
AOM
PPLN
25cm20cm
/2/4
Glanprism
20cmachromat
InSb mode-matching
lenses
ringdowncavity
Andrew MillsWG10
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Cavity Ringdown SpectraCavity Ringdown Spectra
• First results from our DFG laser!
• Clear enhancement of para-H3
+ in para-H2
• More enhanced in argon dilution
• Trot ~ 80 K
– R(1,1)u vs R(2,2)l
ortho-H3+ para-H3
+
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Theoretical PredictionsTheoretical Predictions
• Steady state:
• High temp limit:
• Low temp calculations of k by Park & Light
fp = koppo γ + (koopp+koopo)(1-γ)
(koppo+kppoo)γ + (koopp+koopo+kpoop+kpooo)(1-γ)
fp = α+1+2αγ
3α+2
α hop
exchange
γ [p-H2]
[p-H2]+[o-H2]fp [p-H3
+]
[p-H3+]+[o-H3
+]
koppo k(o-H3+ + p-H2 → p-H3
+ + o-H2)
Park & Light JCP 126, 044305 (2007)
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Comparison with ExperimentComparison with Experiment
Park & Light
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HH33++ toward toward Persei Persei
Savage et al. ApJ 216, 291 (1977)
N(H2) from Copernicus
McCall, et al. Nature 422, 500 (2003)
fp = 0.62 ± 0.09
γ = 0.68 ± 0.20
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Diffuse Clouds ComparisonDiffuse Clouds Comparison
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Future DirectionsFuture Directions
• Experiment– Hollow cathode @ 150 K
• Measure H3+ and H2
– Expansion source• Vary γ, T
• Theory– Different values of α
• Observations– More sources– Improved error bars
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AcknowledgmentsAcknowledgments
http://astrochemistry.uiuc.edu
Tom Geballe(Gemini)
Takeshi Oka(U. Chicago)
NASA LaboratoryAstrophysics
NSF Division of AMO Physics
Brian Tom
Michael Wiczer (→MIT)
Andrew Mills
Kyle Crabtree
Nick Indriolo