Orientation dependence of multiple electron emission processes from diatomic molecules

CARMEN A. TACHINO; MARIEL E. GALASSI; ROBERTO D. RIVAROLA

Kalamazoo, Estados Unidos

Congreso; XXVI International Conference on Photonic, Electronic and Atomic Collisions; 2009

Electron emission from atoms and molecules interacting with  charged particles generates vacancies in the different shells of the target, leading it in a highly excited state. Once the projectile-target interaction is over, these vacancies are occupied by residual target electrons and the energy generated in this process is employed to release photons (radiative transitions) and to emit other bound  electrons (postcollisional Auger-type emission) [1]. The aim of this work is to investigate the effect of Auger-type processes in multiple ionization of diatomic molecules by ion impact. In a previous work, total cross sections for the cases of single-to-fourth ionization degrees of CO molecules by proton impact at intermediate and high collision energies have been analyzed [2].By comparison with existing experimental data it was shown that postcollisional emission dominates the multiple electron ionization reaction at high enough impact energies, and that this effect is more pronounced as the ionization degree increases. Our present objetive is focused on the influence of the projectile nuclear charge on the emission of postcollisional target electrons.To this end, we have described the diatomic molecule as an ensemble of two atoms separated by the molecular equilibrium distance. An independent electron approximation and binomial distributions are employed to calculate cross sections for q-ionization degree, where single ionization probabilities are obtained using the Continuum Distorted Wave-Eikonal Initial State(CDW-EIS) and exponential models. Postcollisional emission probabilities were extracted from the photoionization experimental work of Carlson et al. [3].Theoretical predictions concerning multiple electron emission from CO molecules for impact of He2+ and C6+ ions at intermediate and high projectile velocities are presented. Total cross sections for emission of q-target electrons from direct ionization and from ionization including postcollisional processes have been calculated. A comparison between the present theoretical results and the ones obtained for proton impact shows that, for a particular value of q ata fixed collision energy, the influence of Auger type emission decreases as the projectile nuclear charge is increased. This analysis is extended to cross sections differential in the molecular orientation for impact of 5.9 MeV/u Xe18+ on N2 and O2 targets. The corresponding results are compared with measurements and other theoretical predictions [4].References[1] Auger P 1923, Compt. Rend. 177 169.[2] Tachino C et al. 2008 Phys. Rev. A 77 032714.[3] Carlson T et al. 1966, Phys. Rev. 151 41.[4] Tachino C A, Galassi M E and Rivarola R D 2007, J. Phys.: Conf. Ser. 58 271