Radiative electron attachment to small linear carbon clusters and its significance for the chemistry of diffuse interstellar clouds

Recent spectroscopic studies of carbon chain anions in the gas phase, and m ore specifically of C-7(-) have brought insight into the long-standing myst ery of the unexplained diffuse interstellar bands. Previously, negative ion s had not been considered highly abundant in interstellar clouds, and the q uestion of efficient mechanisms leading to their formation had not been inv estigated in great detail. This work presents a statistical calculation of the rate coefficients for radiative attachment of an electron to small line ar carbon clusters containing 4-9 atoms. We conclude that for molecules wit h 6 or more C atoms, the attachment occurs on every collision at the low te mperatures of diffuse interstellar clouds. (C) 2000 Elsevier Science B.V.