 
Summary: Excitedstate reversible geminate reaction. I. Two different lifetimes
Irina V. Gopich a)
Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk 630090, Russia
Kyril M. Solntsev b) and Noam Agmon
The Fritz Haber Research Center, Department of Physical Chemistry, The Hebrew University, Jerusalem
91904, Israel
~Received 21 July 1998; accepted 22 October 1998!
We obtain an accurate longtime solution for the diffusive kinetics of an excited geminate pair
dissociating reversibly in solution, where the excitedstate lifetimes of the bound and unbound states
may be nonequal. We analyze the longtime asymptotic behavior, finding a transition between two
types of behaviors. In region A, the excited bound pair decays as t 23/2 exp(2t/t 0 8), where t 0 8 is the
lifetime of the unbound state. In region AB, the decay is a pure exponential. At the critical value of
the parameters where the transition occurs, we find a t 21/2 exp(2t/t 0 8) decay. These predictions are
tested against an exact numerical solution of the corresponding coupled partial differential
equations. For region A, we supply an experimental example involving timeresolved excitedstate
proton transfer from 5cyano2naphthol to dimethyl sulfoxide. © 1999 American Institute of
Physics. @S00219606~99!510040#
I. INTRODUCTION
Solutionphase chemistry provides several important ex
amples of reversible diffusioninfluenced reactions in the ex
