Coherence and partial localization in electron emission from HeH$^{+}$ molecular ions

C. A. TACHINO; M. E. GALASSI; F. MARTÍN; R. D. RIVAROLA

Sendai

Conferencia; International Conference on Many Particle Spectroscopy of Atoms, Molecules, Clusters and Surfaces 2010; 2010

Interference effects that can be observed in the electron emission spectra of diatomic molecules are originated by the coherent emission of electrons from the vicinities of the molecular nuclei.  Since the first theoretical description of this effect made by Cohen  and Fano in the decade of 1960 [1], numerous experimental and  theoretical investigations have been carried out. The most part of  these works is dedicated to its study in small homonuclear molecules like H$_{2}^{+}$, H$_{2}$ and D$_{2}$ (for a brief review, see Ref. [2]). Only a few  investigations have been devoted to heteronuclear targets [3,4].In this work, we present the results obtained from the theoretical analysis of the single ionization process of the heteronuclear molecular ion HeH$^{+}$ by ion impact [5]. In the mentioned work, its is shown that fingerprints of coherent emission of electrons from the neighbourhood of the nuclei of this target (which presents a highly asymmetric electron distribution) are visible in the angular distribution of electrons. Two specific spatial orientations of the  target were considered: parallel and perpendicular to the direction of the incident particle. The analysis was made taken into account a coplanar geometry where the emitted electron, the projectile and  the molecule are all in the same plane. The CDW-EIS model was employed to describe the dynamics of the reaction and the final state of the active electron was represented by using a two-effective center approximation.We also show that interferences are still visible even after averaging the angular electron spectra over all molecular orientations. A comparison with results obtained for single ionization of H$_{2}$ targets reveals that the oscillations for the heteronuclear case are less pronounced than for the homonuclear one, being the origin of this behavior attributed to the partial localization of electrons around the alpha particle of the HeH$^{+}$ target [6]. A comparison between the ionization spectra of HeH+ molecular ions by impact of protons and the ones obtained for photoionization with circularly [5] and linearly[6] polarized light shows that they are in qualitative agreement at very high proton energy. The small differences observed in the differential cross sections for the proton and photon cases are attributed to the transfer of momentum induced by the charged projectile, which is absent in the photoionization case.[1] Cohen and Fano, Phys. Rev. 150, 30 (1966).[2] Rivarola, NIMB 261, 161 (2007).[3] Zimmermann et al., Nature Physics 4, 649 (2008).[4] Della Picca et al., Phys. Rev. A 79, 03270 (2009).[5] Tachino et al., J. Phys. B 42, 075203 (2009).[6] Tachino et al., J. Phys. B (accepted for publication).