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Observation Of Nuclear Spin Selection Rules In Supersonically Expanding Plasmas Containing H 3 +

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 +

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Observation Of Nuclear Spin Selection Rules In Supersonically Expanding Plasmas Containing H 3 +

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  1. Observation Of Nuclear Spin Selection Rules In Supersonically Expanding Plasmas Containing H3+ Brian Tom, Michael Wiczer, Andrew Mills, Kyle Crabtree, and Ben McCall Department of Chemistry Department of Astronomy

  2. → + + + + Motivations • 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

  3. Para-H2 + Para-H2+ → Para-H3+ + H • Produce para-H2 n-H2 p-H2 n-H2 p-H2

  4. + + → + + 2e- e- → + + + Para-H2 + Para-H2+ → Para-H3+ + H • Produce para-H2 • Ionize para-H2 • React to para-H3+

  5. H3+ + H2→ (H5+)* → H3+ + H2 1 “identity” H5+ 3 “hop” 6 hop/exchange = 0.5 “exchange”

  6. D2d C2v Dynamics of Reaction C2v ~3000 cm-1 ~1500 cm-1 ~50 cm-1 “hop” “exchange” Not obvious that “statistical” hop/exchange = 0.5 is valid!

  7. Spin-Modification Probability Products formed by Hop and Exchange Reactants Park & Light JCP 126, 044305 (2007)

  8. Spin-Modification Probability Products formed by Hop and Exchange Reactants 1/2  0 ↔ 3/2  1 1/2  0 ↔ 3/2  0 Park & Light JCP 126, 044305 (2007)

  9. Low Temperature Effects • In pure p-H2 • p-H3+→ o-H3+ requires p-H2→ o-H2 ortho I = 3/2 para I = 1/2 ortho I = 1 170 K para I = 0

  10. Cordonnier et al. JCP 113, 3181 (2000) hop ~2.4 exch Oka Group Experiments Pulsed Hollow Cathode reaction not yet measured at low T Positive Column Cell p-H3+ n-H2 p-H2 p-H2→o-H2 o-H3+ p-H3+ o-H3+ p-H2 n-H2 @ 400 K [not 0.5!]

  11. Pinhole flange/ground electrode -450 V ring electrode H3+ Supersonic Expansion Ion Source Gas inlet 2 atm H2 • Developed for DR experiments • H3+ formed near nozzle • [p-H2]/[H2] “frozen” • [p-H3+]/[H3+] evolves, but ~ steady state • Probed by spectroscopy Solenoid valve McCall et al. PRA 70, 052716 (2004)

  12. 2.8 – 4.8 mm DFG System Nd:YAG 1064 nm 532 nm pump laser l/4 Ti:Sapph 700 – 990 nm l/2 AOM 25cm 20cm reference cavity Andrew Mills WG10 l/2 PPLN InSb mode- matching lenses ringdown cavity Glan prism 20cm achromat dichroic

  13. Cavity 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+

  14. hop α exchange [p-H2] γ [p-H2]+[o-H2] [p-H3+] fp [p-H3+]+[o-H3+] koppo γ + (koopp+koopo)(1-γ) α+1+2αγ fp = fp = (koppo+kppoo)γ + (koopp+koopo+kpoop+kpooo)(1-γ) 3α+2 Theoretical Predictions • Steady state: • High temp limit: • Low temp calculations of k by Park & Light koppo k(o-H3+ + p-H2 → p-H3+ + o-H2) Park & Light JCP 126, 044305 (2007)

  15. Comparison with Experiment Park & Light

  16. H3+ toward  Persei fp = 0.62 ± 0.09 McCall, et al. Nature 422, 500 (2003) N(H2) from Copernicus γ= 0.68 ± 0.20 Savage et al. ApJ 216, 291 (1977)

  17. Diffuse Clouds Comparison

  18. Future 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

  19. Acknowledgments Brian Tom Michael Wiczer (→MIT) Andrew Mills Kyle Crabtree Nick Indriolo NSF Division of AMO Physics Takeshi Oka (U. Chicago) Tom Geballe (Gemini) NASA Laboratory Astrophysics http://astrochemistry.uiuc.edu

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