Multiphoton Ionization of Liquid-to-Supercritical Methanol. Ultrafast Dynamics of Electron Localization and Geminate Recombination

摘要

Solvated electrons have been generated by 150 fs, 266 nm multiphoton ionization of methanol and their primary dynamics have been recorded through near-infrared transient absorption over a wide temperature (294 K <= 5 <= 523 K) and pressure (90 bar <= p <= 523 bar) region corresponding to the liquid and the supercritical phases of the solvent. On ultrashort time scales well below a few tens of picoseconds, the dynamics of electron localization, solvation, and thermalization reveal themselves as a delayed rise of the spectroscopic signal originating from the fully equilibrated solvated electron. The temperature-dependence of these dynamics is in line with a thermally-activated process involving hydrogenbond breakage and formation that is induced by the librational/torsional dynamics of the methanol molecules. Longer time scales of up to 1 ns are governed by the dynamics of geminate recombination whose temperature dependence is indicative of multiple competing recombination pathways involving charged and neutral species, including radicals, of yet to be determined nature.