title: Theoretical investigation of nonadiabatic and internal temperature effects on the collision-induced multifragmentation dynamics of Na5+ cluster ions.
abstract: In a continued effort to disentangle adiabatic, nonadiabatic, and internal temperature effects in the collision-induced multifragmentation of alkali-metal cluster ions at moderate energies, we report a theoretical study of this process for the Na5++He encounter in the 100 eV (center-of-mass) collision energy range. The investigation makes use of a diatomics-in-molecules based nonadiabatic molecular-dynamics (NAMD) method. All of the ten electronic 1A' molecular states of the cluster that can be formed by assembling ground-state monomers are considered explicitly. Cross sections for the corresponding 12 possible fragmentation channels are determined. As in the Na4++He case, we find that a few-channel characteristic of adiabatic fragmentation in the electronic ground state dominates. This owes primarily to the dominance of impulsive adiabatic mechanisms. Nonetheless, two significant nonadiabatic transitions take place: electronic excitation during the collision and electronic deexcitation in the postcollision stage. A large amount of the electronic excitation subsequently relaxes into the electronic ground state during the postcollision stage. This important intramolecular vibrational relaxation (IVR)-type mechanism enhances the population of channels characteristic of adiabatic fragmentation in the electronic ground state. The populations of the fragmentation channels are quite sensitive to the internal cluster temperature. This is discussed in terms of the conditions of occurrence of the fragmentation mechanisms and their competition. Comparisons with experimental results are presented and discussed.
authors.affiliation: Laboratoire des Collisions Atomiques et Moléculaires, Unité Mixte de Recherche (UMR 8625), Université Paris-Sud, Centre National de la Recherche Scientifique (CNRS), Fédération de Recherche, Université Paris-Sud, Orsay Cedex, France. sizun@lcam.u-psud.fr
authors.forename: Muriel
authors.initials: M
authors.lastname: Sizun
authors.forename: François
authors.initials: F
authors.lastname: Aguillon
authors.forename: Victor
authors.initials: V
authors.lastname: Sidis