Rovibrational analysis of the XUV photodissociation of HeH + ions

Abstract

We investigate the dynamics of the photodissociation of the helium hydride ion HeH+ by XUV radiation with the aim to establish a detailed comparison with a recent experimental work carried out at the FLASH free electron laser using both vibrationally hot and cold ions. We determine the corresponding rovibrational distributions using a dissociative charge transfer setup and the same source conditions as in the FLASH experiment. Using a nonadiabatic time-dependent wave-packet method, we calculate the partial photodissociation cross sections for the n=1–3 coupled electronic states of HeH+. We find good agreement with the experiment for the cross section into the He + H+ dissociative channel. On the other hand, we show that the experimental observation of the importance of the electronic states with n>3 cannot be well explained theoretically, especially for cold (v= 0) ions. We find a good agreement with the experiment on the relative contribution of the Σ and Π states to the cross section for the He+ + H channel, but only a qualitative one for the He + H+ channel. We discuss the factors that could explain the remaining discrepancies between theory and experiment.