Modeling of adiabatic and diabatic potential energy surfaces of Cl(2P)⋯H2(1∑g+) prereactive complex from ab initio calculations

Abstract

The three lowest diabatic potential energy surfaces for the Cl(2P)+H2(1∑g+) van der Waals complex are derived from accurate ab initio calculations of the T-shaped (C2v) and collinear geometries (C∞v), at the coupled-cluster with the single, double, and noniterative triple excitations level of theory with a large basis set. The nonadiabatic coupling (off-diagonal derivative) matrix element and the fourth, off-diagonal, diabatic surfaces are determined by separate multireference configuration interaction calculations. For the intermediate geometries the angular dependence is modeled by a simple Legendre-polynomial interpolation. Three adiabatic potential energy surfaces (PESs) are also obtained by diagonalizing the total Hamiltonian in the diabatic basis. Both the nonrelativistic and relativistic (including spin–orbit coupling) PESs are evaluated. The nonrelativistic ground state PES agrees well with the entrance channel of the Bian-Werner (BW2) PES [W. Bian and H.-J. Werner, J. Chem. Phys. 112, 220 (2000)]. The dependence on the H2 stretching coordinate is also incorporated.