Entrance Channel Stereospecificity of Photoinitiated H-Atom Reactions in Weakly Bonded Complexes

Hot H-atom reactions photoinitiated in T-shaped C02_HBr and nearly-linear C02-HC1 complexes show remarkably different reaction probabilities. Broadside H-atom approaches in C02~HBr complexes are greatly favoured over the relatively endon approaches of C02~HC1 complexes, a striking steric effect. Photoinitiated hot H-atom reactions with N20 result in a much lower [NH]/[OH] ratio with N20 _HI complexes than under single-collision conditions at the same photolysis wavelength. In addition, OH rotational distributions differ markedly between bulk and complexed conditions, while NH rotational distributions are similar. These results can be interpreted in terms of entrance channel stereospecificity influencing chemically distinct product channels.