Photoionization yield vs energy in H2O and D2O

A simple conductivity jump method was used to measure the escaped solvated electron yield following two-photon excitation of water with Raman-shifted light from an amplified mode-locked Nd:YAG laser. Between 7.8 and 9.3 eV, the quantum efficiency for the escape yields changes from 1.9% to 22%, with an almost exponential dependence on the excitation energy. Quantum efficiency in D2O is smaller and resembles the H2O behavior at 0.35 eV lower energy. The quantum yield measured for one-photon excitation near the water absorption edge at 6.4 eV is a surprisingly large 1.3%. We propose that the mechanism for low energy photoionizaton of water is best described as a dissociative proton-coupled electron transfer to a preexisting trap.