Rates of Photoisomerization of trans-Stilbene in Isolated and Solvated Molecules: Experiments on the Deuterium Isotope Effect and RRKM Behavior

Article abstract of DOI:10.1021/j100271a018

In this paper we consider the dynamics of the photoisomerization of trans-stilbene and related molecules.New measurements of the deuterium isotope effect on reaction rates are presented, and details of RRKM behavior in isolated and solvated trans-stilbene are discussed.From measurements of fluorescence decay rates as a function of the excess vibrational energy in jet-cooled trans-stilbene-d₁₂, an energy threshold to the rates is found at ca. 1200-cm^-1 excess energy in the first excited singlet state.The threshold behavior is similar to that which occurs in the photoisomerization of trans-stilbene-h₁₂.The overall magnitudes of the perdeuterio rates are smaller, however, than the perprotio ones.As with trans-stilbene-h₁₂ themeasured rates are found to be slower than those calculated by standard RRKM theory.Nevertheless, the observed slowing of the rates upon deuteration is predicted by the theory.The results and their interpretation are discussed in light of the results of other jet studies of trans-stilbene derivatives and of studies of the photoisomerization reaction in solution.The role of intramolecular vibrational energy redistribution and the nonadiabatic influences on the reaction are also discussed.