Photoionization of diatomic molecules: effect of coulombic interactions

BOLL, DIEGO IVÁN RENÉ; FOJÓN, OMAR ARIEL

Bariloche

Conferencia; 17th International Conference Physics of Highly Charged Ions; 2014

We study theoretically the photoionization of simple diatomic molecules by an attosecond XUV pulse. We consider XUV polarization parallel and  perpendicular to the internuclear axis as well as circularly polarized XUV  pulses. We show that the multiple differential cross sections (MDCS) obtained by means of an analytical simple model beyond the strong field approximation gives a qualitative agreement with ab initio calculations [1, 2, 3, 4]. In this model, the initial molecular wavefunctions are described as a linear combination of Slater type orbitals (STOs) variationally optimized whereas the final states are represented by separable Coulomb-Volkovtype (SCV) wavefunctions [5].In the case of circular polarization, the MDCS may be seen as a mixture between MDCS with parallel and perpedicular polarization [1,2] plus a torsion term responsible for assymetries [2]. We analize the dependence of this torsion with the description of initial and final states, emphasizing the role of the Coulombic interactions between the ejected photoelectron and theresidual target. We also show that a description of the initial states with a minimal basis is not enough to describe this torsion even qualitatively, posing the need of a careful description of the initial states. Moreover, the role of commonly used approximations, such as the peaking one, is also addressed.Finally, we consider interference effects appearing when the photoionization reaction is assisted by a near infrared laser field. Interestingly, previous interference effects [3,4] predicted for monochromatic pulses persist in the presence of a laser NIR bath leading to a characteristic photoelectron spectrum. By varying the XUV pulse duration, it is possible to span differentmeasurement schemas. We show that the implemented method is able to describe qualitatively the gross features of both the streaking and FELs regimes.