Reaction dynamics of Mg(3 1P1, 4 1S0) with H2: insertion versus harpoon mechanism

We have obtained nascent rotational distributions of MgH (ν = 0 and 1) in the reaction of Mg(4 1S0) with H2. The resultant bimodal features of the MgH distributions are similar to those obtained from Mg(3 1P1). The spectral analysis and potential energy surfaces calculation suggest that the Mg(4 1S0) atom proceeds via a harpoon-type reaction pathway, in contrast to a direct insertion followed by Mg(3 1P1). The Mg(4 1S0) system is closely associated with the Mg(3 1P1)−H2 reaction coordinate, through evolution of a series of surface crossings along the ion-pair coordinate.