The structure and stability of van der Waals complexes of Al with H2

Fragments of the C2v, C∞v, and Cs AlH2 potential energy surfaces have been studied. The kinetic stability of the most stable (2B2) van der Waals complex has been considered with respect to its rearrangement to the lower lying AlH22A1 hydride. The AlH2 (2B2) 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 + H2 dissociation limit. The Cs2A′ potential energy surfaces exhibit very little change in electronic configurations compared with their parent C2v2B2 and2A1 states. This, combined with the high energy of the crossing point, suggests that the probability for the adiabatic reaction AlH2(2B2) →AlH2 (2A1) through an avoided crossing is very low.