AB-INITIO DETERMINATION OF ELECTRONIC-ENERGY SPLITTING AND TRANSITIONRATES FOR NH IN AR MATRICES

The influence of an Ar matrix on the electronic splitting energies of the a1DELTA state of the NH radical and on the radiative transition ra tes of the b1SIGMA+ --> a1DELTA electronic transition is investigated employing two different models for the nearest-neighbor Ar atoms and t aking intramolecular electron correlation of the radical into account. One of the models uses nonpolarizable Ar atoms kept frozen at their s elf-consistent field description, the other one takes their polarizabi lity into account within the framework of a generalized self-consisten t reaction field theory, for which the first calculations employing co rrelated wave functions are reported here. These models are checked wi th regard to their ability to reproduce other ab initio data. The calc ulated splitting energies, combined with the results of calculations o n an embedded NH/Ar(n) cluster using Ar-Ar and state-dependent ab init io Ar-NH pair potentials, allow the assignment of trapping sites of NH in the matrix. The determined transition rates give some insight into the mechanism of matrix-induced enhancement of a dipole-forbidden ele ctronic transition.