The recent detection of the hydrocarbon anion C6H- in the interstellar medium has led us to investigate the synthesis of hydrocarbon anions in a variety of interstellar and circumstellar environments. We find that the anion/neutral abundance ratio can be quite large, on the order of at least a few percent, once the neutral has more than five carbon atoms. Detailed modeling shows that the column densities of C6H- observed in IRC+10216 and TMC-1 can be reproduced. Our calculations also predict that other hydrocarbon anions, such as C4H- and C8H-, are viable candidates for detection in IRC+10216, TMC-1 and photon-dominated regions such as the Horsehead Nebula.
@article{arxiv.0705.0639,
title = {Hydrocarbon anions in interstellar clouds and circumstellar envelopes},
author = {T. J. Millar and C. Walsh and M. A. Cordiner and R. Ní Chuimín and Eric Herbst},
journal= {arXiv preprint arXiv:0705.0639},
year = {2009}
}