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

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

Tokio, Japón

Congreso; XIV International conference on highly charged ions; 2008

Coherent electron emission from diatomic molecular targets provokes the presence of interference patterns in the corresponding spectra of electron ionization. This effect was theoretically predicted more than fourty years ago for the case of photoionization [1]. At the beginning of the present century, 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], confirming the existence of the physical effect. 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 Ref. [3]), in all cases considering homonuclear targets. In the present work, we investigate the possible existence of the effect when a heteronuclear HeH+ molecule is ionized by a fast ion beam. It could be associated with the interference two-slit Young experiment, but where the two orifices have different dimensions. Vibration and rotation of the molecule are considered to be produced in times much larger than the collision time, so that their influences on the studied reaction are neglected. In particular, the internuclear axis is assumed to remain as frozen during the ionization reaction. The orbital of each one of the target electrons in the fundamental state of HeH+ is described by a linear combination of Gaussian functions centred on the positions of the nuclei of the molecule. It allows us to investigate the ionization process within a two-effective centre approximation (TEC; see Ref. [4]), where two effective coulombic continuum functions (associated with each one of the molecular centres) are chosen to describe the interaction of the ejected electron with the residual target in the exit channel. The dynamics of the reaction is analyzed using the Continuum Distorted Wave – Eikonal Initial State model (CDW-EIS), so that the influence of the projectile on the emitted electron is also taken into account. Moreover, into the straight line version of the impact parameter approximation, the interaction of the projectile with the nuclei of the molecule can be easily included [4] when differential cross sections are studied as a function of the momentum transfer. 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. This relatively weak two-centre behaviour is the origin of the presence of interference patterns in differential cross sections. Results corresponding to different collision systems will be presented at the conference. References [1] H. D. Cohen, U. Fano, Phys. Rev. 150 (1966) 30. [2] N. Stolterfoht et al., Phys. Rev. Lett. 87 (2001) 023201. [3] R. D. Rivarola, Nucl. Instr. Meth. B 261 (2007) 161. [4] M. E. Galassi, R. D. Rivarola, P. D. Fainstein, Phys. Rev. A 70 (2004) 032721.