Laser-Induced Real-Time Dynamics of Water Pentamer

We study the earliest steps in the radiolysis of a water pentamer in an intense, 800 nm, linearlypolarized fs laser field [I = (0.1 - 50) center dot 10(14) W/cm(2)] through a real-space, real-time implementation of time-dependent density functional theory nonadiabatically coupled to molecular dynamics. The ionization is enhanced with increasing laser intensity, resulting in the continuous emergence of higher charge states and an increase in the ionization ratio of the deepest levels. Two different reaction pathways of the water pentamer are presented by analyzing the degree of ionization, the level depletion, the probabilities of ionic states, the time-resolved electron density, the bond lengths, and the vibrational frequencies. Both pathways exhibit fluctuations and rearrangement dynamics of the hydrogen bonding network under irradiation. The cyclic structure of the pentamer formed via five oxygen ions is distorted and opened after ionization and tends to maintain a hydronium H3O+ configuration. Proton transfer is accompanied by an oxygen-oxygen contraction and the first proton transfer rate ranges over 6-22 fs.