Geometrical Dependence of photoelectron angular distributions in one electron two center systems

DELLA PICCA, RENATA; FAINSTEIN, PABLO DANIEL; MARTIARENA, MARÍA LUZ; DUBOIS, ALAIN

Freiburg, Alemania

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

Angular distributions of electrons emitted in collisions between photons, electrons and ions with atoms and molecules provide detailed information about the collision dynamics. The photoionization of diatomic molecules with one electronis a process that can be solved exactly and it is thus useful to test different type of approximations commonly employed in collisions with more complicated targets and projectiles.In a recent experimental study of the photofragmentation of the deuterium molecule ~\cite{Nature}, the angular distribution of the emitted electrons was measured for different orientations and internuclear distances of the target molecule. This experiment showed that the angular distribution is highly sensitive to these features and depends markedly on the target wavefunctions.In the present work we perform calculations of H2+ photoelectron angular distributions employing exact one-electron two-center initial and final wavefunctions. We consider different orientations of the polarization vector with respect to the internuclear axis, for several electron energies and for different internuclear distances (R).We first consider the dependence of the angular distributions on theinternuclear distance. For different values of R the single electron calculations show features which qualitatively reproduce the experimental results for photoionization of H2 and of the N2 K-shell.As the internuclear distance for N2 is close to that of H2+ (R = 2 a.u.), there are great similarities in the angular distribution of the photoelectrons emitted from these targets. H2 is quite different as the internuclear distance is much shorter (R = 1.4 a.u.).  However, varying R we can reproduce the behavior of the corresponding angular distributions obtained in experiments and with more sophisticated computational methods \cite{Nuestro,Semenov}.The transition amplitude for photoionization is given by the coherent superposition of \sigma \to \sigma and \sigma \to \pi transition amplitudes with weights dependent on the angle between the internuclear axis and the polarization vector \Theta_\varepsilon.We therefore perform calculations for different values of\Theta_\varepsilon. As an example we show in figure 1 the results for \Theta_\varepsilon =45^\circ. In the figure we show the \sigma \to \sigma (dashed line) and \sigma \to \pi (dash-dotted line) contributions and the full angular distribution (solid line). It is seen from these results that, except when the electric field is parallel (\Theta_\varepsilon =0^\circ) or perpendicular (\Theta_{\varepsilon}=90^\circ) to the molecular axis, there is no propensity for alignment of the angular distribution with either of these two vectors \cite{Nuestro}.