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

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

A GIANT CLOUD

TMC-1 in CCS

MOLECULAR ROTATION “radio” emissions  E = h

MOLECULAR VIBRATIONS Infrared absorption

Cosmic rays produce ions

Radical-Neutral Reactions Radicals: C, CN, CCH 1) Inverse T dependence 2) Large rate coefficients by K: k ~ 10(-10) cm 3 s -1

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 + +… Precursor to ammonia, hydrocarbons CH + O  CO + H

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

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

Steady-state analysis of H 3 +

Steady-state analysis of H 2 D + Actually, D/H abundance ratios less time-dependent than actual concentrations in absence of accretion.

Deuterium Fractionation Species Fractionation Model NH 2 D HDCO DCN DCO N 2 D CH 3 OD

Agreement with TMC-1 nsm

Source of Difficulty Rapid neutral-neutral reactions not studied in the laboratory; for example, O + C 3  CO + C 2 ????? C + C 3  C 4 + h ?????

TMC-1 Gas-grain models with nsm