Two-photon ionization and dissociation of liquid water by powerful laser UV radiation

The effect of two-photon absorption of powerful laser UV radiation by liquid water has been investigated. The two-photon absorption coefficients were measured at a number of wavelengths from 266 to 316 nm. Using a method of picosecond spectroscopy it is shown that the absorption of two UV quanta with λ = 266 nm by water results in its ionization with a quantum yield of 15% or in its dissociation with a quantum yield of 13%. The dependence of the quantum yield of ionization on the UV radiation wavelength has been obtained. The measured ionization limit of liquid water is 6.5 eV. The products of two-photon laser photolysis of water were studied. The reaction of water with the soluted oxygen resulting in superoxide ion (O 2 − ) formation is shown to be the main transformation of the hydrated electron e aq − . Other, less effective, channels of e aq − transformation are reactions resulting in the formation of the hydroxyl ion (OH − ). The measured lifetime of e aq − is0.3 μs. The relative contribution of e aq − , OH 2 − , O 2 − and H 3 O + to the photoconductivity of water under powerful UV laser radiatio been studied.