ERIC HERBST DEPARTMENTS OF PHYSICS, CHEMISTRY AND ASTRONOMY THE OHIO STATE UNIVERSITY Interstellar Chemistry: Triumphs & Shortcomings
Molecules seen in UV,visible, & IR absorption Diffuse Matter
Molecules seen in IR absorption and radio emission 10 K 10(4) cm-3 H2 dominant sites of star formation Dense Interstellar Clouds
+ small grains and PAH’s
O
Cosmic rays produce ions
FORMATION OF GASEOUS WATER H 2 + COSMIC RAYS H e Elemental abundances: C,O,N = 10(-4); C<O H H 2 H H H O OH + + H 2 OH n + + H 2 OH n H H 3 O + + e H 2 O + H; OH + 2H, etc
FORMATION OF HYDROCARBONS H C CH + + H 2 CH n + + H 2 CH n H; n=1,2 CH H 2 CH h CH e CH 4 + H (5%) CH 3 + 2H (70%) CH CO CH 4 + HCO +
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
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!!
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!
Chemistry imperfect!!
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
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)
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)
WANTED! CHEMISTS Quantum chemists (potential surfaces) Dynamicists (reaction rates) Spectroscopists Surface scientists Theorists & Experimentalists!!