Selected-ion flow tube methods applied to the bracketing of proton affinities. PA(C 2N 2) and PA(HC 3N)

Abstract

A selected-ion flow tube (SIFT) apparatus fitted with an electron impact ion source has been used to produce protonated species XH + by direct electron impact, by reaction of X + with H 2, and by reaction of H 2 + with X. The three methods of XH + production were applied in the bracketing of the proton affinities of cyanogen, C 2N 2, and cyanoacetylene, HC 3N, with measurements of rate constants for proton-transfer reactions of XH + with C 2N 2 and HC 3N and of C 2N 2H + and H 2C 3N + with X. Comparisons with established proton affinities for X provide values for PA(C 2N 2) = 162±2 kcal mol −1 and PA(HC 3N) = 184±4 kcal mol −1. The latter result is in disagreement with a previous flowing afterglow determination.