Electron transfer mediated decay in HeLi₂ cluster: Potential energy surfaces and decay widths

Electron transfer mediated decay (ETMD) is a process responsible for double ionization of dopants in He droplets. It is initiated by producing He⁺ in the droplet, which is neutralized by ETMD, and has been shown to strongly enhance the dopant's double ionization cross section. The efficiency of ETMD, the spectra of emitted secondary electrons, and the character of the ionic products depend on the nuclear dynamics during the decay. To date, there has been no theoretical investigation of multimode dynamics which accompanies ETMD, which could help to understand such dynamics in a He droplet. In this article, we consider the He-Li₂ cluster where an ab initio examination of multimode dynamics during the electronic decay is feasible. Moreover, this cluster can serve as a minimal model for Li₂ adsorbed on the droplet's surface-a system where ETMD can be observed experimentally. In He droplets, Li₂ can be formed in both the ground X¹Σ_g ⁺ and the first excited a³Σ_u ⁺ states. In this article, we present ab initio potential energy surfaces of the electronic states of the He-Li₂ cluster involved in ETMD, as well as the respective decay widths. We show that the structure of these surfaces and expected nuclear dynamics strongly depend on the electronic state of Li₂. Thus, the overall decay rate and the appearance of the observable electron spectra will be dictated by the electronic structure of the dopant.