			15min:

THE ABUNDANCE OF C₇^- IN DIFFUSE INTERSTELLAR CLOUDS.

D. P. RUFFLE, R. TERZIEVA, E. HERBST, Departments of Physics and Astronomy, and Chemical Physics Program, The Ohio State University, Columbus, OH 43210.

It has recently been proposed that C₇^- is a carrier of five of the numerous diffuse interstellar bands. In this talk, we report an attempt to reproduce the required abundance of C₇^- relative to hydrogen of 4 × 10^-8 through the use of various models for the chemistry in diffuse clouds. Our models incorporate large neutral and charged linear hydrocarbons, and contain the time-dependent desorption of seed molecules from grain surfaces. We are able to find conditions that lead to the production of the required fractional abundance of C₇^- but only for short periods of time in an astronomical sense.