Predissociation effects in the A, B, and C states of CH and the interstellar formation rate of CH via inverse predissociation

Abstract

Predissociation effects in the lowest excited electronic states of CH have been studied in detail via lifetime measurements using the high frequency deflection technique. This high-resolution technique has enabled us to make lifetime measurements of a large number of individual rotation- vibration levels, in some cases even of individual A components, and has revealed that all levels of the A, B, and C states above the ground state dissociation limit undergo observable predissociation. The newly discovered predissociation of the A state has an interesting anomaly, and has a rate that is two orders of magnitude smaller than that of the C state. However, this small rate yields an interstellar CH inverse predissociation rate that could be comparable with the direct radiative association rate. The two-component short lifetimes (5 and 18 ns) of the C state, reported by other workers, are shown to originate from the different V' = 0 and V' = 1 states, rather than from the two spin components of the V' = 0 levels, and we find no long lifetime (8( ns) component. Subject headings: interstellar: molecules - molecular process - transition probabilities