Threshold Law for the Probability of Excitation of Molecules by Photon Impact. A Study of the Photoionization Efficiencies of Br2, I2, HI, and CH3I

Abstract

A study is made of two types of excitation process in molecules, leading to either dissociation to an ion-pair, or to autoionization. The latter process, in the case of the iodine-containing molecules, clearly makes a very significant contribution to the total ionization. The threshold law for the probability of excitation by photon impact is shown to be approximated closely by a delta function of the excess energy. Energy values are measured for various states of the molecules, and are in good agreement with available spectroscopic data. The electron affinities of Br and I are found to be 3.53±0.12 and 3.13±0.12 ev, respectively.