NONADIABATIC DYNAMICS AND ELECTRONIC-ENERGY RELAXATION OF CL(P-2) ATOMS IN SOLID AR

The dynamics of Cl(P-2) atoms in a solid Ar matrix is studied, with em phasis on electronic energy relaxation of excited states, and on p-orb ital reorientation effects. The method used follows Tully's approach f or nonadiabatic molecular dynamics simulations, which treats the elect ronic degrees of freedom quantum-mechanically, and the atomic motions classically, allowing for ''hopping'' of the atoms between different p otential energy surfaces. We introduce an extended version of this met hod, to handle ''Berry Phase'' effects due to the doubly degenerate Kr amers pairs of states present in this system. The role of both electro static and of spin-orbit interactions between different electronic sta tes is incorporated in the treatment. The simulations yield a time sca le of 13 ps for the energy relaxation of the highest excited electroni c state of Cl(P-2). A time scale of similar magnitude is found for the depolarization of this state. However, the time scale for orbital reo rientation at thermal conditions is only 0.7 ps. This is attributed to the fact that at thermal conditions, only the two lowest electronic s tates are populated. The physical mechanisms of these basic radiationl ess decay processes are discussed on the basis of the simulations. (C) 1996 American Institute of Physics.