A PAIR POTENTIALS STUDY OF MATRIX-ISOLATED ATOMIC ZINC - II - INTERSYSTEM CROSSING IN RARE-GAS CLUSTERS AND MATRICES

The mechanism of 4p P-1(1)-->4p P-3(J) intersystem crossing (ISC) foll owing excitation of the 4p P-1(1) level of matrix-isolated atomic zinc is investigated using a pair potentials approach. This is achieved by extending earlier ISC calculations on the Zn . RG(2) and Zn . RG(3) c omplexes to the square planar Zn . RG(4) and square pyramidal Zn . RG( 5) species which are the building blocks of the Zn . RG(18) cluster us ed to represent the isolation of atomic zinc in the substitutional sit e of a solid rare-gas host. ISC predictions in these clusters are base d on whether crossing of the strongly bound (1)A(1) states, having a 3 p P-1(1) atomic asymptote, occurs with the repulsive E-3 states correl ating with the 4p P-3(J) atomic level of atomic zinc. Predictions base d on (1)A(1)/E-3 curve crossings for E-3 states generated with the cal culated ab initio points for the Zn . RG (3)Sigma(p(z)) states do not agree with matrix observations. Based on similar overestimation of ISC in the Zn . RG diatomics, less repulsive Zn . RG (3)Sigma(p(z)) poten tial curves are used resulting in excellent agreement between theory a nd observations in the Zn-RG matrix systems. (1)A(1)/E-3 curve crossin gs do not occur in the Zn-Ar system which shows only singlet emission. Curve crossings are found for the Zn-Xe system which exhibits only tr iplet emission. The Zn-ES system does not show a crossing of the body mode Q(2), which exhibits a strong singlet emission at 258 nm while th e waist mode Q(3), does have a crossing, resulting in a weak singlet e mission at 239 nm and a stronger triplet emission-at 312 nm. The effic iency of ISC is determined from Landau-Zener estimates of the surface hopping probabilities between the (1)A(1) and the E-3 states. Differen ces in the application of this theory in the gas and solid phase are h ighlighted, indicating that the rapid dissipation of the excited-state energy which occurs in the solid must be included to obtain agreement with observations. (C) 1998 American Institute of Physics. [S0021-960 6(98)00532-7]