Temperature dependence of the quenching of Mg(3P J) by H2: Evidence for a change from physical to chemical exit-channel control

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Abstract
The rate constant for the quenching of Mg(3s3p 3PJ) by H2 increases sharply with temperature in the 612–841 °K range. A simple equation is shown to fit this data as well as a rate‐constant value reported by Taieb and Broida at lower temperature: This two‐term expression results from the assumption that inefficient E to V, R energy transfer occurs in competition with a chemical exit channel in which there is no activation barrier beyond the 11.5 kcal/mole endothermicity of the reaction: Mg(3PJ)+H2→MgH+H. A transfer therefore occurs from physical to chemical exit‐channel control in this unusual case as the temperature is increased.