title: 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 Hn (+) systems (n = 3-5). The method uses a generalized Hellmann-Feynman theorem applied to a multi-state description based on diatomics-in-molecules (for H3 (+)) or triatomics-in-molecules (for H4 (+) and H5 (+)) 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 H2(v(')=0,j(')=0)+H2 (+)(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 H2 (+) are calculated and compared with the available experimental data, yielding an excellent agreement. The effect of vibrational excitation of H2 (+) 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.
authors.affiliation: Departamento de Química Física Aplicada (UAM), Unidad Asociada IFF-CSIC, Facultad de Ciencias C-XIV, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Sanz-Sanz
authors.affiliation: Departamento de Química Física Aplicada (UAM), Unidad Asociada IFF-CSIC, Facultad de Ciencias C-XIV, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Aguado
authors.affiliation: Instituto de Física Fundamental, CSIC, C/ Serrano, 123, 28006 Madrid, Spain.
authors.forename: Octavio
authors.initials: O
authors.lastname: Roncero
authors.affiliation: Faculty of Science, UOIT, Oshawa, Ontario L1H 7K4, Canada.
authors.forename: Fedor
authors.initials: F
authors.lastname: Naumkin