The abundance of C(7)over-bar in diffuse clouds

It has recently been proposed that C-7(-) is a carrier of five of the numerous diffuse interstellar bands. In this paper, we report an attempt to reproduce the required abundance of C-7(-) relative to hydrogen of n(C-7(-)) similar to 1 x 10(-9)n(H) through the use of various models for the chemistry in diffuse clouds. Our model network contains large neutral and charged linear hydrocarbons and incorporates the time-dependent desorption of seed molecules from grain surfaces. We find a limited set of physical and chemical conditions that result in the required fractional abundance of C-7(-) but only for rather short periods of time.