Relevance of dissociative molecular states for resonant two-center photoionization of heteroatomic dimers

Abstract

Photoionization of a weakly bound van-der-Waals dimer, composed of two atomic species A and B, is studied theoretically. Atom A can be ionized either directly or via an indirect two-center channel, where atom B is first resonantly photoexcited and, afterwards, transfers the excitation energy via long-range electron–electron correlations radiationlessly to atom A, causing its ionization. By taking the vibrational nuclear motion of the dimer during the process into account, we analyze the contributions to the photoionization cross section from bound and dissociative molecular states in the final –B system. For the specific example of a LiHe dimer we show (a) that substantial contributions to both ionization mechanisms result from dissociative Li He states and (b) that the two-center pathway strongly dominates over the direct photoionization channel for photon energies close to one of the molecular LiHe resonances.