Double ionization of the hydrogen chloride molecule: Influence of the target orientation on multiple differential cross sections

We report in this work multiple differential cross sections for the double ionization of isolated hydrogen chloride molecules impacted by electrons. The calculations are performed within the first Born approximation by considering a target molecular state described by means of a single-center molecular wave function. In the initial state, the incident electron is described by a plane wave, while in the final state Coulomb wave functions are used for modeling the interaction between the two ejected electrons and the residual target ion, the scattered electron being described by a plane wave. Additionally, a Gamow factor is introduced to take into account the Coulomb repulsion between the two outgoing particles. The contributions to the various differential cross sections of the four outermost orbitals of the hydrogen chloride molecule, namely, 4σ, 5σ, 2πx, and 2πy, are then reported for specific target orientations and by considering only the case of two electrons ejected from the same molecular orbital. The obtained results point out the effect of the target orientation on both the (e, 3e) and the (e, 3 − 1e) collisions and clearly evidence the signature of the well-known double ionization mechanisms, namely, the shake-off and the two-step 1 processes for all the cases investigated.