Breakdown of Kramers theory description of photochemical isomerization and the possible involvement of frequency dependent friction

Abstract

We present new data on the ground state isomerization rate of DODCI and compare our results to previously obtained excited state data. We find that the one-dimensional Kramers expression does not fit the data over the whole viscosity range when the friction is measured by either the overall rotation time or the solvent viscosity. The deviation is qualitatively similar to that previously observed in diphenyl butadiene when the viscosity was used as the friction measure. Deviations from the simple hydrodynamic theory appear to depend on the reduced frequency for isomerization. We show how our results are consistent with the one-dimensional Kramers theory when a frequency dependent friction is used to describe the influence of the solvent.