Photoinduced ultrafast nonequilibrium dynamics in liquid water

Understanding photoexcitation dynamics in liquid water is of crucial significance for both fundamental scientific explorations and technological applications. However, the ultrafast nonequilibrium dynamics are hard to track due to extreme complexity of laser−water interaction and the ultrafast timescale. I will present the theoretical simulations of photoinduced nonequilibrium electronic and structural dynamics in liquid water, including water plasma generation, high-harmonic generations and hydrogen productions. I) The intense laser pulses violently excite liquid water and lead to severe molecular dissociation and plasma generation during the laser pulses. The laser-induced water plasma is characterized by a high fraction of free protons (∼50%), nonequilibrium ionic and electronic distributions and a metallic electronic density of states. II) The oscillating electric fields also drive the periodic oscillations of electronic currents in liquid water, and the extreme nonlinear processes give rise to high-harmonic generations (HHG) in liquid systems. The water plasma generation can be directly tracked via time-resolved HHG with a femtosecond resolution. The plasma generation leads to the decrease of cutoff energy E_c and enhanced decoherence in HHG. III) The water plasma in warm-dense state constitutes a superior reaction environment for hydrogen production, and the cooling of water plasma is demonstrated to lead to the generation of various molecules, e.g., H₂, O₂, and H₂O₂ molecules.