REACTION DYNAMICS OF MG(3S3P(1)P(1)) WITH H-2

We measured the temperature dependence of rotational population distri bution of the nascent product MgH((2) Sigma(+)) in the reaction of Mg( 3s3p(1)P(1)) with H-2. The results indicate that the reaction is domin ated by an Mg-insertive mechanism, consistent with the isotope effect reported previously. We also presented the vibrational population dist ribution, and thereby found that two parallel reaction pathways are re sponsible for the subject reaction following Mg-H-2 collision in a ben t configuration. The major one produces MgH in higher rotational level s and comparable v '' = 0 and v '' = 1 populations, while the other mi nor one produces MgH in low rotational levels and preferentially v '' = 0. By means of a two-dimensional potential energy surface(PES) calcu lation, a deep insight into the reaction pathways has been gained. The resulting PES's information reveals the possibility of a nonadiabatic transition between the excited B-1(2) PES and the ground PES. The ben t intermediate MgH2 near the surface crossing starts trajectories eith er smoothly following the dissociation coordinate of Mg-H distance or attractively falling down through a linear HMgH geometry before breaki ng apart. The former trajectory accounts for the minor reaction pathwa y to produce MgH, while the latter one responses to the major reaction pathway. The impact of isotope and temperature effects on MgH can als o be readily explained with use of the calculated PES's.