1. ERIC HERBST DEPARTMENTS OF PHYSICS, CHEMISTRY AND ASTRONOMY THE OHIO STATE UNIVERSITY Interstellar Chemistry: Triumphs & Shortcomings

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

3. Molecules seen in IR absorption and radio emission 10 K 10(4) cm-3 H2 dominant sites of star formation Dense Interstellar Clouds

5. + small grains and PAH’s

6. O

7. Cosmic rays produce ions

8. FORMATION OF GASEOUS WATER H 2 + COSMIC RAYS  H 2 + + e Elemental abundances: C,O,N = 10(-4); C<O H 2 + + H 2  H 3 + + H H 3 + + O  OH + + H 2 OH n + + H 2  OH n+1 + + H H 3 O + + e  H 2 O + H; OH + 2H, etc

9. FORMATION OF HYDROCARBONS H 3 + + C  CH + + H 2 CH n + + H 2  CH n+1 + + H; n=1,2 CH 3 + + H 2  CH 5 + + h CH 5 + + e  CH 4 + H (5%)  CH 3 + 2H (70%) CH 5 + + CO  CH 4 + HCO +

10. FORMATION OF O 2,N 2 CO OH + O  O 2 + H **** OH + N  NO + H NO + N  N 2 + O CO, N 2 + He +  C +, N + +… CH + O  CO + H

12. RADICAL-NEUTRAL RX (CONT) CN + C 2 H 2  HCCCN + H CCH + HCN  HCCCN + H YES NO CCH + C 2 H 2  C 4 H 2 + H YES Barrier cannot be guessed!!

13. Latest network – osu.2003 – contains over 300 rapid neutral-neutral reactions. Rate coefficients estimated by Ian Smith and others for many of these. Verification needed!! Solved kinetically; thermodynamics useless!

14. Chemistry imperfect!!

15. SOME CRITICALLY NEEDED STUDIES 1) atom (O, C) – neutral reactions e.g. O + C4  CO + C3 2) unimolecular isomeric exchange e.g. HCN*  HNC* 3) radiative association 4) recombination without dissociation? e.g. C60+ + e  C60

16. SURFACE CHEMISTRY 1) Mechanisms (diffusive [Langmuir- Hinshelwood], Eley-Rideal, hot atom, impurity site) 2) Dependence on size, mantle, fluffy nature 3) Rate equations vs. stochastic treatments 4) non-thermal desorption (cosmic rays)

17. Some Outstanding Astrochemical Problems How to make gas-phase models more robust How to construct gas-grain models and predict mantle abundances accurately How to model the chemistry of star- and planet-forming regions (heterogeneity and time dependence)

18. WANTED! CHEMISTS Quantum chemists (potential surfaces) Dynamicists (reaction rates) Spectroscopists Surface scientists Theorists & Experimentalists!!