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[7.07] Reactions of C_n^- and C_nH^- with Atomic and Molecular Hydrogen

T.P. Snow, C. Barckholtz, V.M. Bierbaum (University of Colorado)

Gas phase reaction rate constants have been measured for the reactions of C_n^- (n = 2, 4-10) and C_nH^- (n = 2, 4, 6, 7) with atomic hydrogen in a flowing afterglow-selected ion flow tube (FA-SIFT) at room temperature and 0.5 Torr of helium pressure. In general, the rate constants are relatively fast, but are less than the collisional rate (\approx 10^-9 cm³ s^-1). All C_n^- and C_nH^- ions react by associative-detachment (e.g. C_n^- + H arrow C_nH + e^-) and the C_n^- for n \geq„ 7 also react by association (e.g. C_n^- + H arrow C_nH^-). Reaction of these carbon chain anions with molecular hydrogen was found to be too slow to measure in our instrument (k < 10^-13 cm³ s^-1). We are continuing these studies by measuring reaction rates for other abundant neutrals (such as atomic oxygen and atomic nitrogen) with carbon chain anions, and will report the results of these measurements.

We gratefully acknowledge the National Aeronautics and Space Administration for support of this research, through NASA grant NAG5-6758 to the University of Colorado.

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