Nonadiabatic molecular dynamics of photoexcited Li2+Nen clusters
Résumé
We investigate the relaxation of photoexcited Li2+ chromophores solvated in Nen clusters (n = 2–22) by means of molecular dynamics with surface hopping. The simplicity of the electronic structure of these ideal systems is exploited to design an accurate and computationally efficient model. These systems present two series of conical intersections between the states correlated with the Li++Li(2s) and Li++Li(2p) dissociation limits of the Li2+ molecule. Frank–Condon transition from the ground state to one of the three lowest excited states, hereafter indexed by ascending energy from 1 to 3, quickly drives the system toward the first series of conical intersections, which have a tremendous influence on the issue of the dynamics. The states 1 and 2, which originate in the Frank–Condon area from the degenerated nondissociative 12∏u states of the bare Li2+ molecule, relax mainly to Li++Li(2s) with a complete atomization of the clusters in the whole range of size n investigated here. The third state, which originates in the Frank–Condon area from the dissociative 12∑u+ state of the bare Li2+ molecule, exhibits a richer relaxation dynamics. Contrary to intuition, excitation into state 3 leads to less molecular dissociation, though the amount of energy deposited in the cluster by the excitation process is larger than for excitation into state 1 and 2. This extra amount of energy allows the system to reach the second series of conical intersections so that approximately 20% of the clusters are stabilized in the 22∑g+ state potential well for cluster sizes n larger than 6.