Collision-induced dissociation of interstellar molecules

A theory of the collision-induced dissociation of molecules in a low-density gas is presented, and calculations of the dissociation rate coefficients are carried out. The theory suggests that large differences occur in the dissociation rates of homonuclear and heteronuclear molecules in astrophysical environments, differences which are of diagnostic utility in distinguishing between shocked and heated regions of the interstellar gas. The calculated dissociation rate coefficients are considerably smaller than those suggested by a simple extrapolation of laboratory data. The theory has an important bearing on the ability of molecules to survive the passage of shocks, and affects significantly the thermal and chemical response of the shocked interstellar gas.