Abstract
A thorough time-independent quantum scattering study is performed on a benchmark potential energy surface for the H+Li2 reaction at the fundamental electronic state. Integral and differential cross sections are calculated along with thermal rate coefficients until convergence is reached. Our findings show that vibrational and rotational excitations of the reactant hinder reactivity, though for the latter a considerable reaction promotion was spotted as we increase the reactant rotational quantum number until the critical value of j = 4. Such a promotion then begins to retract, eventually becoming an actual inhibition for larger j. In a straightforward manner, the concept of time-independent methods implemented in this study allowed this accurate state-to-state analysis. Furthermore, a nearly isotropic behaviour of the scattering is noted to take place from the angular point of view. Remarkably, our computational protocol is ideally suited to yield converged thermal rate coefficients, revealing a non-Arrhenius pattern and showing that J-shifting approach fails to describe this particular reaction. Our results, when compared to previous and independent ones, reinforce the latest theoretical reference for future validation in the experimental field.
Highlights
Cross beam experiments were performed for chemical reactions among hydrogen atoms and (K2, Rb2 or Cs2) alkali homonuclear diatoms, and they all revealed considerable enthalpy variations
Aiming to obtain the integral cross sections, we had to externally develop a FORTRAN code that would basically perform the transformations of Eqs (7) and (8) prior to proceeding to the summation described by Eq (10)
It can be stated that sufficiently close theoretical agreement has been reached with the minor exception of the original data published by ref.[26], which brought results laying way below the average, the use of quasi-classical trajectories (QCT) might have seemed advisable given that the characteristics of the Li2 H potential energy surface (PES) did not suggest a considerable tunneling contribution
Summary
Cross beam experiments were performed for chemical reactions among hydrogen (or deuterium) atoms and (K2, Rb2 or Cs2) alkali homonuclear diatoms, and they all revealed considerable enthalpy variations. These observations allowed Lee, Gordon and Herschbach[3] to infer a valuable analogy between such processes and the dynamics of the deuteron, an important projectile in nuclear physics. This study concluded that the formation of LiH molecules which are ro-vibrationally excited by an amount of energy comparable to −ΔH in the particular H+Li2 bimolecular exchange reaction is somewhat favored, a feature observed in similar reactions involving other alkali diatoms like K2, Rb2 and Cs23. Still in the time-dependent formalism and on the same PES proposed in ref.[28], Zhu, Dong and Li32 employed the wave packet method with a second order split operator in order to obtain state-to-state resolved quantities, having observed that forward and backward scattering signals peaked at the two extreme angles
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