Reaction Dynamics of Mg(3s3p¹P₁) with H₂

Abstract

We measured the temperature dependence of rotational population distribution of the nascent product MgH(2∑+) in the reaction of Mg(3s3p1P1) with H2. The results indicate that the reaction is dominated by an Mg‐insertive mechanism, consistent with the isotope effect reported previously. We also presented the vibrational population distribution, and thereby found that two parallel reaction pathways are responsible for the subject reaction following Mg‐H2 collision in a bent configuration. The major one produces MgH in higher rotational levels and comparable v″ = 0 and v″ = 1 populations, while the other minor one produces MgH in low rotational levels and preferentially v″ = 0. By means of a two‐dimensional potential energy sur‐face(PES) calculation, 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 1B2 PES and the ground PES. The bent intermediate MgH2 near the surface crossing starts trajectories either smoothly following the dissociation coordinate of Mg‐H distance or attractively falling down through a linear HMgH geometry before breaking apart. The former trajectory accounts for the minor reaction pathway to produce MgH, while the latter one responses to the major reaction pathway. The impact of isotope and temperature effects on MgH can also be readily explained with use of the calculated PES's.

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

“…Potential energy surfaces (PES) calculation also indicates that the reactive coordinate along the 1B 2 surface in C2v geometry is attractive, while the collinear approach suffers from a substantial energy barrier [6]. Our recent study of a two-dimensional PES calculation reveals that the reactive surface of the excited state crosses non-adiabatically to the ground state, on which the MgH 2 intermediate complex begins to break apart through two possible trajectories leading to the MgH(2~+) and H products [8,9]. A corresponding quasiclassical trajectory calculation lends support to the above prediction [9].…”