Reactions of Cn- and CnH- with atomic and molecular hydrogen

Gas-phase reaction rate constants have been measured for the reactions of C(n)(-) (n = 4-10) and C(n)H(-) (n = 2, 4, 6, 7) with atomic hydrogen in a flowing afterglow-selected ion flow tube 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 (similar to 10(-9) cm(3) s(-1)). All C(n)(-) and C(n)H(-) ions react by associative detachment (e.g., C(n)(-) + H --> C(n)H + e(-)), and the C(n)(-) for n greater than or equal to 7 also react by association (e.g., C(n)(-) + H --> C(n)H(-)). Reaction of these carbon chain anions with molecular hydrogen was found to be too slow to measure in our instrument ( k < 10(-13) cm(3) s(-1)).