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ERIC HERBST DEPARTMENTS OF PHYSICS, CHEMISTRY AND ASTRONOMY THE OHIO STATE UNIVERSITY

Gaseous Chemistry in Interstellar Space. ERIC HERBST DEPARTMENTS OF PHYSICS, CHEMISTRY AND ASTRONOMY THE OHIO STATE UNIVERSITY. Diffuse Matter. Molecules seen in UV,visible, & IR absorption. A GIANT CLOUD. TMC-1 in CCS. MOLECULAR ROTATION. “radio” emissions. D E = h n.

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ERIC HERBST DEPARTMENTS OF PHYSICS, CHEMISTRY AND ASTRONOMY THE OHIO STATE UNIVERSITY

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  1. Gaseous Chemistry in Interstellar Space ERIC HERBST DEPARTMENTS OF PHYSICS, CHEMISTRY AND ASTRONOMY THE OHIO STATE UNIVERSITY

  2. Diffuse Matter Molecules seen in UV,visible, & IR absorption

  3. A GIANT CLOUD

  4. TMC-1 in CCS

  5. MOLECULAR ROTATION “radio” emissions DE = hn

  6. MOLECULAR VIBRATIONS Infrared absorption

  7. Cosmic rays produce ions

  8. Radical-Neutral Reactions Radicals: C, CN, CCH 1) Inverse T dependence 2) Large rate coefficients by 10-50 K: k~ 10(-10) cm3 s-1

  9. FORMATION OF GASEOUS WATER H2 + COSMIC RAYS  H2+ + e Elemental abundances: C,O,N = 10(-4); C<O Elemental abundances: C,O,N = 10(-4); C<O H2+ + H2 H3+ + H H3+ + O  OH+ + H2 OHn+ + H2  OHn+1+ + H H3O+ + e  H2O + H; OH + 2H, etc

  10. FORMATION OF HYDROCARBONS H3+ + C  CH+ + H2 CHn+ + H2  CHn+1+ + H; n=1,2 CH3+ + H2  CH5+ + hn CH5+ + e  CH4 + H (5%)  CH3 + 2H (70%) CH5+ + CO  CH4 + HCO+

  11. FORMATION OF O2 ,N2 CO OH + O  O2 + H OH + N  NO + H NO + N  N2 + O CH + O  CO + H CO, N2 + He+ C+, N+ +… Precursor to ammonia, hydrocarbons

  12. Latest network – osu.2003 – contains over 300 rapid neutral-neutral reactions. Rate coefficients estimated by Ian Smith and others. Deuteration requires networks twice as large!!! Other networks: nsm, Rate99

  13. At earlier times, abundances for many small species close to steady state values.

  14. Steady-state analysis of H3+

  15. Steady-state analysis of H2D+ Actually, D/H abundance ratios less time-dependent than actual concentrations in absence of accretion.

  16. Deuterium Fractionation Species Fractionation Model NH2D 0.011 0.020 HDCO 0.059 0.055 DCN 0.011 0.025 DCO+ 0.02 0.062 N2D+ 0.08 0.052 CH3OD 0.027 0.030

  17. Agreement with TMC-1 nsm

  18. Source of Difficulty • Rapid neutral-neutral reactions not studied in the laboratory; for example, • O + C3 CO + C2????? • C + C3  C4 + hn?????

  19. TMC-1 Gas-grain models with nsm

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