Interference patterns in spectra of electron ionization of heteronuclear HeH+ targets in interaction with fast ion beams.

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

Kalamazoo, Estados Unidos

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

Interference patterns have been observed in the resulting electron spectra when diatomic targets are ionized. This interference effect was theoretically predicted more than fourty years ago by Cohen and Fano for the case of photoionization [1]. An experimental confirmation of its existence was obtained at the beginningof the present century, when oscillations appearing in double differential cross sections were measured by the first time for impact of fast multiply charged heavy ions on H2 targets [2]. Theeffect was atributed to coherent electron emission from the vicinities of each one of the nuclei of the molecular target. This was an incentive for further active experimental and theoretical research, not only for photon and ion beams but also for electron beams (for a brief review, see reference [3]).The aim of this work is to investigate the possible existence of interference effects when a heteronuclear HeH+ molecule is ionized by a fast ion beam. In the present reaction, rotational and vibrational molecular times are considered to be much larger than the collision one, so that their influences are neglected and in consequence it can be assumed that the internuclear axis remains as frozen during the ionization process. A Slater Type Orbital-6 Gaussian basis set (STO-6G) is employed to describe the orbital of each one of the target electrons in the fundamental state of HeH+ [4, 5]. The initial bound electron wavefunction presents a strong monocentric character. The electrons are placed mostly around the alpha particle but however they have a smaller probabilitity to remain at the proximities of the proton center. In the exit channel a two-effectivecenter approximation (TEC; see reference [6]) is employed. In this approximation two effective coulombic continuum functions associated with each one of the molecular centers are chosen todescribe the interaction of the ejected electron with the residual target. The dynamics of the reaction is analyzed using the Continuum Distorted Wave-Eikonal Initial State model (CDWEIS),so that the influence of the projectile on the emitted electron is also taken into account. In spite of the weak two-center character ofthe electron orbital in the initial state it is shown that interference patterns appear in the electron spectra corresponding to coplanar geometry reactions. They are associated in this work with molecular ionization by circularly polarized photons inciding perpendicular to the plane formed by the molecular axis and the emitted electrons.References[1] Cohen H D and Fano U 1966, Phys. Rev. 150 30.[2] Stolterfoht N et al. 2001, Phys. Rev. Lett. 87 023201.[3] Rivarola R D 2007, Nucl. Instr. Meth. B 261 161.[4] O-ohata K, Taketa H and Huzinaga S 1966, J. Phys. Soc. Japan 21 2306.[5] Hehre W J, Stewart R F and Pople J A 1969, J. Chem. Phys. 51 2657.[6] Galassi M E, Rivarola R D and Fainstein P D 2004, Phys. Rev. A 70 032721.