Influence of the Reactants Rotational Excitation on the H + D₂(v = 0, j) Reactivity

Abstract

We have analyzed the influence of the rotational excitation on the H+D 2 (υ=0, j) reaction through quantum mechanical (QM) and quasiclassical trajectories (QCT) calculations at a wide range of total energies. The agreement between both types of calculations is excellent. We have found that the rotational excitation largely increases the reactivity at large values of the total energy. Such increase cannot be attributed to a stereodynamical effect but to the existence of recrossing trajectories that become reactive as the target molecule gets rotationally excited. At low total energies, however, recrossing is not significant and the reactivity evolution is dominated by changes in the collision energy; the reactivity decreases with the collision energy as it shrinks the acceptance cone. When state-to-state results are considered, rotational excitation leads to cold product's rovibrational distributions, so that most of the energy is released as recoil energy.

Comparative dynamics of the two channels of the reaction of D + MuH

“…Moreover, the height of the barrier in the collinear vibrational n 1 = 0, 1 adiabatic path, and not through the 3D barrier, was found to provide a classical threshold for the reaction. A tentative explanation for this effect was suggested in a previous work 9 in terms of a weak coupling of the symmetric stretch with the reaction coordinate. Hence, the quantum state corresponding to this mode would be much better defined than that of the bending mode, which is strongly coupled to the motion along the minimum energy path.…”

“…The vibrationally adiabatic potentials necessary to evaluate DE b for the different isotopic variants of the H + H 2 reaction were computed using the ABCRATE code. 31 As discussed in previous works, 9,12 there are no QM thresholds for exoergic reactions even in the presence of a barrier. However, it is convenient to define an operational or an effective threshold in order to compare with classical results.…”

“…[5][6][7] Quasiclassical trajectory (QCT) calculations combined with a Gaussian binning procedure, capable of accounting for the large zero point energy of the products, also succeeded in reproducing the experimental KIE, which suggests that tunneling plays a secondary role 6 in the Mu + H 2 reaction. The detailed analysis of the theoretical results [5][6][7][8][9] showed that the appreciable endoergicity of the Mu + H 2 reaction (D r H o 0 = 0.32 eV), due to the high zero point energy (ZPE) of the MuH product and, to a lower extent, the resulting increase in the vibrationally adiabatic barrier width, is basically responsible for the low reactivity of this isotopic variant and thus for the observed KIE. A comparable KIE with respect to Mu + H 2 is obtained for the exoergic D + H 2 6 and thermoneutral H + H 2 10 isotopic variants of the reaction.…”

Rate Coefficients and Kinetic Isotope Effects of the XCl + Cl (X=H, D, Mu) Reactions from Ring Polymer Molecular Dynamics

“…It is the shortest lived and the lightest hydrogen isotope composed of positive ions and electrons (Mu=μ + e -). It is the most sensitive probe for quantum mass effects in chemical reactions [21,22]. This system is a typical heavy-light-heavy mass combination with the transfer of hydrogen atom.…”

Rate Coefficients and Kinetic Isotope Effects of the Cl + XCl  XCl + Cl (X=H, D, Mu) Reactions from Ring Polymer Molecular Dynamics

“…It is the shortest lived and the lightest hydrogen isotope composed of positive ions and electrons (Mu=μ + e -). It is the most sensitive probe for quantum mass effects in chemical reactions [20,21]. This system is a typical heavy-light-heavy mass combination with the transfer of hydrogen atom.…”