Non-adiabatic couplings and dynamics in proton transfer reactions of Hn+ systems: Application to H2+H2+→H+H3+ collisions

Abstract

Analytical derivatives and non-adiabatic coupling matrix elements are derived for H + n systems (n = 3-5). The method uses a generalized Hellmann-Feynman theorem applied to a multi-state description based on diatomics-in-molecules (for H + 3 ) or triatomics-in-molecules (for H + 4 and H + 5 ) formalisms, corrected with a permutationally invariant many-body term to get high accuracy. The analytical non-adiabatic coupling matrix elements are compared with ab initio calculations performed at multi-reference configuration interaction level. These magnitudes are used to calculate H 2 (v ′ = 0, j ′ = 0) + H + 2 (v, j = 0) collisions, to determine the effect of electronic transitions using a molecular dynamics method with electronic transitions. Cross sections for several initial vibrational states of H + 2 are calculated and compared with the available experimental data, yielding an excellent agreement. The effect of vibrational excitation of H + 2 reactant and its relation with non-adiabatic processes are discussed. Also, the behavior at low collisional energies, in the 1 meV-0.1 eV interval, of interest in astrophysical environments, is discussed in terms of the long range behaviour of the interaction potential which is properly described within the triatomics-in-molecules formalism. C 2015 AIP Publishing LLC. [http://dx

Low temperature reaction dynamics for CH3OH + OH collisions on a new full dimensional potential energy surface

“…In this work we use a method recently proposed37–39 which consists in dividing the electronic Hamiltonian in two terms as H=Hdiab+HMB. H diab is an electronic diabatic matrix, in which each diagonal matrix element describes a rearrangement channel. In the case of H4+ and H5+ these terms were described by a triatomics-in-molecules method (TRIM)37,38, which is an extension of the diatomics-in-molecule (DIM)40,41, while in the case of H 2 CO+OH those terms were described by force fiels 39, as an extension of the reactive force field (RFF) approach42. This allows to describe polyatomic fragments rather accurately and long-range interactions can be included explicitly.…”

Non-adiabatic Quantum Dynamics of the Dissociative Charge Transfer He++H2 → He+H+H+

“…To analyze the accuracy of the fit, we compare the analytical non-adiabatic coupling matrix elements (NACMEs) in the adiabatic representation, obtained from the fitted diabatic energies and coupling, with the ab initio results calculated using the MOLPRO program package (Werner et al, 2018). As done previously for H4+ and H5+ in Sanz-Sanz et al (2015), the analytical NACMEs can be calculated from the generalized Hellmann-Feynman theorem,…”

“…where Ĥ el is the electronic Hamiltonian and the rhsm is obtained from the derivatives of the diabatic energies V ij (Sanz-Sanz et al, 2015). Ab initio calculations have been performed using the Multi-Reference Configuration-Interaction method, with the aug-cc-pVTZ basis set of Dunning (1989) and Woon and Dunning (1994).…”

A Ring Polymer Molecular Dynamics Approach to Study the Transition between Statistical and Direct Mechanisms in the H2 + H3+ → H3+ + H2 Reaction

“…The full dimensional potential by Aguado et al 44 is used here to study the reaction dynamics. This potential includes analytical derivatives45 and it properly describes the permutation symmetry and long range asymptotic behavior. We use the RPMDrate code46 developed by one of us (YVS) and modified for direct trajectories approach which consists of two steps, thermalization and real-time dynamics.…”