Isotope Effects in the Photoionization Yields and in the Absorption Cross Sections for Methanol, Ethanol, Methyl Bromide, and Ethyl Bromide

Abstract

The values of the absorption cross section σ and the photoionization yield η (the probability that photon absorption produces ionization) have been experimentally determined for CH₃OH and CD₃OD, C₂H₅OH and C₂D₅OD, CH₃Br and CD₃Br, and C₂H₅Br and C₂D₅Br at various photon energies in the energy range of 9.97–11.78, 10.32–11.78, 10.08–11.78, and 9.97–11.78 eV, respectively. In each case, there is increased ionization for the deuterated molecule over a part of the energy range studied. This increase is seen in the values of both η and the photoionization cross section, ${\sigma }_i{\mathrm{(\sigma }}_i\mathrm{=\eta \; \sigma )}$ , and it is discussed as evidence for the competitive preionization of intermediate states. The effects of methyl substitution on σ and σ_i are also discussed, and ionization potentials are reported for each gas.