The structure and stability of van der Waals complexes of Al with H-2

Fragments of the C-2v, C-infinity y, and C-s AIH(2) potential energy surfaces have been studied. The kinetic stability of the most stable (B-2(2)) van der Waals complex has been considered with respect to its rearrangement to the lower lying AIH(2) (2)A(1) hydride. The Al-H-2 (B-2(2)) complex is found to be kinetically stable. The lowest energy crossing between these states is estimated to occur at about 30 kcal/mol above the Al + H-2 dissociation limit. The C-s (2)(2)A' potential energy surfaces exhibit very little change in electronic configurations compared with their parent C-2v B-2(2) and 2A, states. This, combined with the high energy of the crossing point, suggests that the probability for the adiabatic reaction Al-H-2 (B-2(2)) --> AlH2 ((2)A(1)) through an avoided crossing is very low. (C) 1997 Elsevier Science B.V.