A Model for Energy Deposition in Liquid Water

Abstract

both a redistribution of oscillator strengths relative to the gas phase, and the possible existence of a collective oscillation (plasmon). We investigate the effects of such a plasmon on the partition of energy deposited by fast electrons. To accomplish this, we develop a heuristic model of the liquid based primarily upon the extensive body of gas phase generalized oscillator strength data. The model has one major free parameter, the strength of the 21.4 eV plasmon. Using standard resonance shapes to approximate the energy loss spectrum of the plasmon, we estimate that the water plasmon has an oscillator strength of 2 (+J about 0.6) and a half-width of about 3.5 eV. We then calculate the slowing down of an electron in liquid water according to continuous-slowing-down theory, and after allowing for plasmon decay, compare the yields for the liquid and gas phases. Our results indicate that when the plasmon decays by ionization it produces a spectrum of only subexcitation electrons. We find a modest change in the yields with the eV per-ion-pair lowered from 30.7 in the gas to 28.5 in the liquid.