Interference effects in single electron ionization of diatomic molecules by fast ion impact

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

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

 Since the decade of 1960, when pioneer investigations about the coherent electron emission from diatomic molecules were published, a great amount of experimental and theoretical researchs related to interference effects have been carried out. The majority of these works were done considering simple molecular targets such as H$_{2}^{+}$, H$_{2}$ and D$_{2}$ (see Ref. [1] for a brief review). There are a relatively  scarce number of works that analyze the presence of this effect in the electron spectra of more complicated molecules such as N$_{2}$, O$_{2}$, CO [2-4]. A main problem with these kind of targets is that they present several molecular orbitals (MO), and the electronic emission can occur from any of them. In consequence, the ionization cross sections must be computed taking into account the partial contributions from each MO. Moreover, each individual molecular orbital will present its own interference pattern. In [3] and [4], where single ionizaton of N$_{2}$ and O$_{2}$ molecules by ion impact was experimentally analyzed, the authors attributed the origin of the oscillations that appear in ionization cross sections to second-order effects related to intramolecular scattering. This conclusion is based on the analysis of the oscillation frequencies, which are in close agreement with the ones characteristic of secondary interferences. According to these authors, no evidence of primary Young-type interferences appears.In the present investigation, we extend our previos works [5,6] to theoretically analyse the possibility of the existence of interference patterns for diatomic molecules with more than one molecular  orbital in the fundamental state. The CDW-EIS model and a two-effective center approximation are employed to describe the dynamics of the reaction and the final state of the active electron in the continuum of the heavy particles, respectively. We consider a coplanar geometry where the emitted electron, the projectile and the molecule are all in the same plane. In this approximation, the angular distribution of electrons is computed for two particular molecular orientations -parallel and perpendicular to the direction of the incident particle. Also, double differential cross sections as a function of the energy and the angle of emission of the electron -obtained by averaging the angular spectra over all molecular orientations- are shown.[1] Rivarola, NIMB 261, 161 (2007).[2] Zimmermann et al., Nature Physics 4, 649 (2008).[3] Baran et al., J. Phys. Conf. Series 58, 215 (2007); Phys. Rev. A 78, 0,12710 (2008).[4] Winkworth et al., J. Phys. Conf. Series 163, 012044 (2009); NIMB 267, 373 (2009).[5] Tachino et al., J. Phys. B 42, 075203 (2009).[6] Tachino et al., J. Phys. B (accepted for publication).