The temperature dependences of some types of gaseous ionic reactions of astrochemical interest.

The rate constants of ion-molecule reactions which are of potential significance in astrochemical systems are found to exhibit significant, and in many cases, negative temperature dependences. The rate constants of fast ion-polar molecule reactions (e.g., XH+ + B leads to BH+ + X) may increase by a factor of 5-10 between 1000 and 10D. Slow reactions that proceed via reaction complexes (e.g., H- transfer and association reactions) often exhibit temperature dependences of the form k = AT-n, n = 1-5. Both transition state theory considerations and the coupled-oscillator RRK-type model are seen to be able to account qualitatively for the behavior of slow ion-molecule reactions.