ON THE KINETIC ASPECTS OF EXCIPLEX FORMATION UNDER MOLECULAR SUPERSONIC BEAM CONDITIONS

The existence of various orientational isomers in the ground and excit ed states of electron-donor-acceptor molecular systems under molecular supersonic beam conditions has been confirmed in a number of experime nts. The analysis of the potential energy surfaces of such systems sug gests that the photokinetic scheme of formation of an exciplex (charge -transfer excited state) should be modified (beyond the classical two- state model) and should also include, among the others, the relaxation pathways of excited Franck-Condon structures corresponding to various ground-state orientational isomers of a Van der Waals complex. A modi fied kinetic scheme is proposed, solved and applied to analysis of ava ilable experimental data. Computer simulations of the time profiles of exciplex emission have shown that the proposed photokinetic scheme is capable of handling qualitatively different features of the rise and decay curves observed for different electron-donor-acceptor systems un der molecular supersonic beams conditions. (C) 1997 Elsevier Science B .V.