Nascent internal energy distributions of MgH(MgD) produced in the reaction of Mg(3s3p1P1) with H2(D2)

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Abstract
Nascent rotational quantum‐state distributions of MgH(v=0,1) and MgD(v=0) have been determined for the reactions Mg(1P1)+H2→MgH+H, Mg(1P1)+D2→MgD+D. The distributions are bimodal, with the major components (∼90%) peaking at very high rotational quantum numbers and the minor components at approximately N=10. The MgH(v=1)/MgH(v=0) ratio is 0.7±0.2, and there is decreasing population in the higher vibrational levels. The ‘‘high‐N’’ distribution is discussed in terms of energy release from bent MgH2 configurations resulting from preferential ‘‘side‐on,’’ insertive attack of H2 by Mg(1P1). This is shown to be consistent with ab initio calculations of the relevant MgH2 potential surfaces. The deconvoluted high‐N distribution for MgD(v=0) is closer to phase‐space‐theory predictions than is that for MgH(v=0), and it is suggested that HMgH and DMgD intermediates are formed with lifetimes nearly long enough for internal randomization of vibrational energy to occur. The minor ‘‘low‐N’’ component could well be due to inefficient ‘‘end‐on’’ attack of the H–H bond by Mg(1P1), but because of the complexities of the potential surfaces other possible explanations are discussed. The inefficient disposal of energy into vibration indicates very ‘‘late’’ energy release. Finally, detailed comparisons are made between these results and analogous studies of the reaction O(1D2)+H2→OH+H, and several striking similarities are noted.