Ab initio potential energy surface for the Ar(S-1) plus OH(X-2 Pi) interaction and bound rovibrational states

Adiabatic potential energy surfaces for the (2)A(') and (2)A(') states of t he Ar(S-1)-OH(X(2)Pi) complex were calculated using supermolecular unrestri cted fourth-order Moller-Plesset perturbation theory and a large correlatio n consistent basis set supplemented with bond functions. The potential ener gy surface (PES) of the A(') state has two minima. The global minimum from the unrestricted coupled-cluster calculations with single, double, and noni terative triple excitations occurs for the collinear geometry Ar-H-O at R=7 .08a(0) with a well depth of D-e=141.2 cm(-1). There is also a local minimu m for the skewed T-shaped form, whereas the Ar-O-H arrangement corresponds to a saddle point. The PES of the A(') state also has two minima, which occ ur for the two collinear isomers. A variational calculation of the bound ro vibrational states was performed. The calculated binding energy, D-0=93.8 c m(-1), and the energies of the bound vibrational states are in good agreeme nt with experiment [see Berry , Chem. Phys. Lett. 178, 301 (1991) and Bonn , J. Chem. Phys. 112, 4942 (2000), preceding paper]. (C) 2000 American Inst itute of Physics. [S0021-9606(00)01211-3].