Characterization of Photoionization Intermediates via ab Initio Molecular Dynamics

Abstract

Ab initio molecular dynamics (AIMD) allows one to probe complex potential energy surfaces at finite temperatures. Here we extend this technique to the analysis of vertical excited states along ground-state AIMD trajectories. We illustrate this idea via comparison to the silver trimer anion photoionization experiments of Boo et al. (J. Phys. Chem. 1997, 101, 6688). This work displayed an aberrant trend in the ionization efficiency near threshold, which suggests the presence of an intermediate state resonance. We present an AIMD simulation at the complete active space self-consistent field level of the silver trimer anion photoionization to ground-state neutral silver trimer for several different basis set expansions. We have analyzed the excited-state manifold via multireference singles and doubles configuration interaction (MRSDCI) and complete active space second-order perturbation theory (CASPT2) calculations performed at representative points along the neutral silver trimer trajectories in order to discern the nature and relative energy of the intermediate excited-state probed in the experiment. We find an excited state that may coincide with the possible resonance state accessed by the ∼400 nm probe and a higher near-linear excited state that may have been accessed by the ∼270 nm probe in the photoionization experiments.