Torsional dynamics of molecules on barrierless potentials in liquids. II. Test of theoretical models

Abstract

The theoretical predictions of three theories for large amplitude dynamics on a barrierless excited state potential are tested. The predicted forms for the time dependent integrated excited state population are compared with experimentally measured excited state absorption decays of crystal violet in various solvents. We have generalized the early theory of Oster–Nishijima [J. Am. Chem. Soc. 78, 1581 (1956)] to allow for arbitrary placement of the initial excited state population relative of the nonradiative sinks which couple the flat excited state potential to the ground state. An analytic form for decay of the integrated excited state population is derived for this generalized flat potential model. In addition we have found that the predictions of Forster–Hoffmann [Z. Phys. Chem. NF 75, 63 (1971)] cannot be made to fit the experimentally measured excited state decays of crystal violet. Finally we show that the theory of Bagchi–Fleming–Oxtoby [J. Chem. Phys. 78, 7375 (1983)] can fit the decays observed in various solvents fairly well. The best fits, however, are obtained using the generalized flat potential model.