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

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, σi(σi=η σ), and it is discussed as evidence for the competitive preionization of intermediate states. The effects of methyl substitution on σ and σi are also discussed, and ionization potentials are reported for each gas.