A chemical dynamics, kinetics, and theoretical study on the reaction of the cyano radical (CN; X2Σ+) with phenylacetylene (C6H5CCH; X1A1)

Abstract

The chemical reaction dynamics to form o-, m-, and p-cyanophenylacetylene via the neutral–neutral reaction of ground state cyano radicals with phenylacetylene and D1-phenylacetylene were investigated in crossed beam experiments; these studies were combined with kinetics measurements of the rate coefficients at temperatures of 123, 200, and 298 K and supplemented by electronic structure calculations. The data suggest that the reaction is initiated by a barrier-less addition of the electrophilic cyano radical to the o-, m-, or p-position of the aromatic ring. The eventually fragmented via atomic hydrogen elimination to form o-, m-, and p-cyanophenylacetylene via tight exit transition states with the hydrogen atom being ejected almost perpendicularly to the molecular plane of the rotating complex. The overall reaction to form o-, m-, and p-cyanophenylacetylene was found to be exoergic by 89 ± 18 kJ mol−1 in nice agreement with the calculations. The o-cyanophenylacetylene isomer is of particular relevance as a potential building block to the formation of nitrogen-substituted didehydronaphthalene molecules in analogy to didehydronaphthalene in Titan's aerosol layers—a pathway hitherto neglected by the planetary science modeling community.