1999ApJ...523..678R

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)∼1x10^–9n_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.