15min:

ERIC HERBST, Departments of Physics, Astronomy & Chemistry, The Ohio State University, Columbus, OH 43210; TOM MILLAR, MARTIN CORDINER, CATHERINE WALSH, Queen's University Belfast, Belfast, Northern Ireland, UK; ROISIN NI CHUIMIN, Astrophysics Group, The University of Manchester, Manchester M60 1QD, UK.

Now that the first molecular anion, C₆H^-, has been detected in the cold dark cloud TMC-1 and both this ion and C₄H^- detected in the circumstellar envelope IRC+10216 based on the laboratory work of Thaddeus and co-workers, it is of interest to study anew how anions are produced and destroyed via gas-phase reactions in interstellar and circumstellar environments. Relatively abundant anions are most likely formed principally by radiative attachment and depleted by photodetachment and ion-molecule reactions with atomic hydrogen and oxygen. New estimates of rate coefficients for some of these processes have been made. We have then included formation and depletion pathways for a number of molecular anions in the latest UMIST database for astronomy (http://www.udfa.net/). With this enhanced network, theoretical abundances and column densities of the anions in TMC-1 and IRC+10216 have been calculated. Our results will be discussed, along with our views on the most likely new anions to be detected once laboratory data become available.