CHEMICAL REACTIONS IN THE O(1D) + HCl SYSTEM I.

Abstract

New global ab initio potential energy surfaces (PES) are presented for the low-lying 11A′, 11A′′ and 21A′ electronic states which are correlated to O (1D) + HCl . These potential energy surfaces are computed by using the multi-reference configuration interaction method with the Davidson correction (MRCI+Q). The reference functions are constructed by the complete active space self-consistent field (CASSCF) calculations using the quadruple zeta + polarization basis set augmented with diffuse functions. The computations are carried out at about 5000 molecular conformations on each three-dimensional potential energy surface. The high accuracy of the computations is confirmed by a comparison with the available most accurate data for the ground state 11A′; thus the present work is the first report of the accurate potential energy surfaces for the two excited states. Three low-lying transition states on the excited surfaces, two (TS2 and TS4) on 11A′′ and one (TS3) on 21A′, are found. Since TS2 and TS3 are as low as 0.07 eV and 0.28 eV, respectively, and correlate to the OH (2Π) + Cl (2P) product, these excited surfaces are expected to play quite important roles in the reaction dynamics. Possible effects of nonadiabatic couplings among the three PESs are also briefy discussed, although the nonadiabatic couplings have not yet been estimated. The quantum reaction dynamics on these three PESs are discussed in the second accompanying paper, Paper II.