Potential energy surfaces for and energetics of the weakly-bound Al-H-2 and B-H-2 complexes

Following an earlier investigation [M. H. Alexander, J. Chem. Phys. 99, 601 4 (1993)] of the B(2s(2)2p P-2)-H-2 complex, we report new ground state pot ential energy surfaces (PESs) for the Al(2s(2)2p P-2)-H-2 and B(2s(2)2p P-2 )-H-2 van der Waals complexes, based on multireference configuration-intera ction calculations with an extrapolation to the complete basis set limit. T he degeneracy of the Al 3p and B 2p orbitals gives rise to three adiabatic PESs (two of A' symmetry and one of A' symmetry in C-s geometry). By viewin g the two adiabatic states of A' symmetry as an orthogonal transformation o f the in-plane Al 3p and B 2p orbitals, we transform the PESs to an approxi mate diabatic representation, which involves four potential energy function s. Both molecules have energy minima in C-2v geometry with an electronic sy mmetry B-2(2). The dissociation energies are D-e = 231 cm(-1) for Al-H-2 an d 142 cm(-1) for B-H-2. The energies of the lowest bend-stretch levels of t he complexes of Al (P-2) and B (P-2) with either o- or pH(2) are determined from the diabatic PESs. The predicted zero-point-corrected dissociation en ergies (D-0) are 49.2 and 74.3 cm(-1) for Al with pH(2) and oH(2), respecti vely, and 39.7 and 59.8 cm(-1) for B with pH(2) and oH(2), respectively. (C ) 2000 American Institute of Physics. [S0021-9606(00)30213-6].