Ultrafast Dynamics of Chlorine−Water and Bromine−Water Radical Complexes Following Electron Photodetachment in Their Anionic Precursors

Abstract

Picosecond dynamics initiated by electron photodetachment in Cl-···H2O and Br-···H2O complexes is explored using classical Wigner trajectories which correctly map the initial quantum vibrational state of the systems. The three lowest potential energy surfaces of the neutral clusters reached after electron photodetachment are constructed by the ab initio Fock-Space Coupled Cluster Method and then quantitatively fitted to a Diatomics-in-Molecule Model which also allows for a simple inclusion of spin−orbit interactions. Because of large differences between the shapes of the anionic and neutral potential energy surfaces, and due to the presence of light hydrogen atoms, an unusual dynamical behavior is observed. Although the vertical photodetachment process places the systems above the dissociation threshold, the clusters do not dissociate directly. Instead, relatively long-lived vibrational resonances are observed. This is due to a strong excitation of the nondissociative (internal) water rotation and only a weak excitation of the dissociative intermolecular stretch upon photodetachment. Implications of the observed dynamics for the interpretation of experimental vibrationally resolved ZEKE spectra are discussed.