Quantitative Representation of Specific Rate Constants k(E) for the Photoisomerization of Diphenylpolyenes: The Solution of a Longstanding Problem

Abstract

Specific rate constants k(E) of the photoisomerization of four isotopomers of trans-stilbene, of 4-chloro-(4CS) and 4-methyl-trans-stilbene (4MS), of all-trans-1,4-diphenyl-1,3-butadiene (DPB), and of 4-(dimethylamino)-4‘-cyanostilbene (DCS) are represented by conventional RRKM theory, using new ab initio calculations of excited state frequencies. Data from supersonic beam experiments are reproduced quantitatively when the barrier heights are fitted to the experiments and activated complex frequencies are taken unchanged from the parent molecules. The main difference to earlier work lies in the smaller frequencies now calculated for the reaction coordinates. The results of this work clearly support an adiabatic mechanism of the reaction which can very well be quantified by statistical unimolecular rate theory.