 
Summary: Threedimensional simulations of reversible bimolecular reactions.
II. The excitedstate target problem with different lifetimes
Alexander V. Popova)
and Noam Agmonb)
Department of Physical Chemistry and the Fritz Haber Research Center, The Hebrew University,
Jerusalem 91904, Israel
Received 20 March 2002; accepted 4 June 2002
We report a first microscopic simulation for the diffusional kinetics of a reversible excitedstate
reaction, A B AB, where A and AB have different lifetimes and the Bparticles are in excess.
When the excited species equilibrate fast compared with the excitedstate lifetimes, one obtains the
preequilibrium approximation. The full timedependence in this case is approximated by a shifted
infinitelifetime expression, and this allows us to derive an analytic expression for the asymptotic
exponent. Multiplying this exponential is a t 3/2
term. When the excitedstate decay of AB is fast,
we obtain the quasistationary approximation. Quantitative comparison between various theories and
simulation is presented. © 2002 American Institute of Physics. DOI: 10.1063/1.1496455
I. INTRODUCTION
Bimolecular reactivity in solution is more complex than
most chemists care to admit. The chemical rate equations1
describe a special limit when diffusion is very fast as com
