Tetramethylene lifetimes predicted by microcanonical variational unimolecular rate theory

We have used variational RRKM theory to predict the lifetime of the tetramethylene biradical as a function of total energy, in order to compare with the recent experiments of Pedersen, Herek and Zewail (PHZ). Frequencies and relative energies were taken from our previously published canonical variational study. We find that the predicted lifetime lies within or slightly below the range reported by PHZ, but the experimentally observed energy dependence of the lifetime is much larger than can be accommodated by variational RRKM theory.