TARGET ORIENTATION DEPENDENCE IN ION–MOLECULE COLLISIONS AT INTERMEDIATE AND HIGH ENERGIES

C.A TACHINO; M.E. GALASSI; R. RIVAROLA

Freiburg, Alemania

Congreso; 25 International Conference on Photonic, Electronic and Atomic Collisions (XXV ICPEAC); 2007

    Multiple ionization processes in ion-molecule collisions have been a matter of active research in the last decades [1], due to their interest inmany areas such as astrophysics, hadrontherapy and radiobiology.    The recent development of new experimental facilities has allowed to obtain an almost complete mapping, in the momentum space, of theaggregates resulting from the collision [2]. Furthermore, at high enough impact energies the vibrational and rotational times of the moleculartarget are much greater than the collision one, and so it can be assumed that the spatial orientation of the molecule remains fixed during theinteraction between projectile and target [3].    In the present work, multiple ionization of diatomic molecules as a function of the orientation of the molecular axis is studied, at inter-mediate and high collision energies. The target molecule is described as two independent atoms separated by the equilibrium internuclearmolecular distance. The Independent Particle Model (IPM) is employed, where probabilities of q-fold ionization are calculated using binomialdistributions [4]. Impact parameter probabilities for single-ionization are obtained applying different approximations: the Continuum Distorted Wave-Eikonal Initial State (CDW-EIS) [5] and the Exponential (EM) models [6], the last one using Hartree-Fock of effective atomic shell radii as the interaction distance.    CDW-EIS differential cross sections adequately describe existing experimental data [7] as can be observed in figure 1 for impact of 5.9MeV/u Xe18+ on O2 . The depression in differential cross sections at θ = 90◦ can be attributed to the fact that closer encounter collisions become dominant as q increases.    Comparisons with experiments and theoretical predictions for other collision systems will be also shown.References[1] R. Rivarola and P. Fainstein, Nucl. Inst. Methods B 205, 448 (2003).[2] J. Ullrich and V. Shevelko, Many Particle Quantum Dynamics in Atomic and Molecular Fragmentation (Berlin: Springer, 2003).[3] M. Galassi et al., Phys. Rev. A 70, 032721 (2004).[4] T. Kirchner et al., Phys. Rev. A 65, 042727 (2002).[5] M. Galassi et al., J. Phys. B 35, 1727 (2002).[6] C. Caraby et al., Phys. Rev. A 55, 2450 (1997).[7] B. Siegmann et al., Phys. Rev. A 65, 010704 (2002); Nucl. Inst. Methods B 205, 629 (2003).