Ab initio studies on photochemical reactions of Al atoms with H2 molecules

Potential energy surfaces are computed for the five lowest electronic states of the Al + H2 system in its symmetric nuclear arrangement. Mechanisms of photochemical reactions of Al atoms with H2 molecules are proposed, based on the calculated potential energy surfaces. The insertion reaction of the ground-state Al atom into the H2 molecule is difficult under normal conditions. However, photoexcited Al atoms are capable of reacting with H2 molecules along different pathways. The results obtained are consistent with experimental findings. The potential energy profiles of the dissociation reaction, AlH2 → AlH + H, are traced by employing the UMP2 energy gradient method. Photocexcited Al atoms react with H2 molecules along the 2 2A1 state pathway, and the AlH2(2Σg+) formed dissociates easily into AlH(1Σ) and H(2S). The dissociation reaction of ground-state AlH2 is difficult.