Energy distribution and cross section for photoionization in polar liquids

Abstract

A method is devised for the experimental determination of the dependence of the cross section on photon energy for bound-continuum transitions of species dissolved in polar liquids of low vapor pressure. The method is based on the determination of energy distribution curves (EDC) for photoelectron emission (PEE) into the gas phase above the solution. Theoretical analysis covers EDC distortion by electron-molecule collisions in the gas phase and resulting experimental requirements; derivation of a general equation for EDC's; criterion for the superposition of the descending segment of EDC's at different photon energies; and determination of cross section. Experimental results on PEE by the anthracene anion radical A− in hexamethyl phosphoric triamide include the effect of pressure on EDC's from 0.4 × 10−3−3.4 × 10−3 torr at different photon energies and the effect of photon energy on EDC's at 0.4 × 10−3 torr from 475 to 240 nm. Analysis of data covers effect of pressure; validity of the method for obtaining cross sections; determination of the cross section for transition to the continuum; correlation with the PEE process via autoionization. The approach developed here may prove feasible for a variety of systems.