Photoionization Cross Sections and Asymmetry Parameters for the Valence Shell of Methanol

Abstract

Theoretical cross sections for photoionization of the methanol valence orbitals in covering a region up to 80 eV beyond the first ionization potential are reported. The molecular quantum defect orbital, MQDO, method, which has proved to be reliable in previous applications to molecular photoionization, has been used. To our knowledge, predictions of electronic partial cross section profiles on this molecule are made here for the first time, and we are not aware of any reported experimental data. Partial cross sections for production of parent and fragment ions of methanol have also been calculated and compared with previous measurements. In addition, the MQDO method has been used to calculate the angular distribution of photoelectrons for the valence orbitals of methanol over the 11-50 eV photon energy range. Our results are compared with experimental data, showing a good agreement in most cases. We hope that the present results might be of use in atmospheric and interstellar chemistry, where this molecule plays an important role.

Valence Photoelectron Spectra of Liquid Methanol and Ethanol Measured Using He II Radiation

“…A stable fit was achieved, yielding relative peak areas similar to those of the gas phase for all bands (see Table ). While liquid-phase ionization cross sections are unknown, it is not expected that there is any large variation as compared to the gas phase (gas values are found in ref and refs therein). All liquid bands are shifted toward lower VIEs (higher eKEs) as indicated by diagonal dashed lines in Figure and summarized as Δ E g–l in Table .…”

Fragmentation of interstellar methanol by collisions with He˙+: an experimental and computational study

“…The photodissociation of methanol upon single photon absorption in the gas phase has been amply studied both experimentally 45,[58][59][60][61][62] and theoretically. 63 Relative or absolute photoionization CSs for the production of both the molecular and fragment ions have been measured in the VUV region, from the ionization threshold 58,59 up to 80 eV, 45 as well as in the X ray region, 64 using Photoelectron Photoion Coincidence (PEPICO) spectroscopy 60,61,64 and dipole (e, e + ion) spectroscopy. 45 The most relevant study to compare with present results is from Burton et al, 45 where photoionization efficiencies and ionic photofragmentation BRs have been measured/calculated up to 80 eV.…”

Excitation energies, photoionization cross sections, and asymmetry parameters of the methyl and silyl radicals

“…We have also determined the photoelectron asymmetry parameters as a function of photoelectron energy for the ionization of the outermost valence orbitals of the methyl and silyl radicals. In recent applications to molecules containing firstrow elements, 26,27 the comparison of the MQDO asymmetry parameters with experimental results showed the reliability of the computational method. The present calculations predict a Cooper minimum in the asymmetry parameter profile of the silyl radical.…”