A. Hamnett

Photoelectron branching ratios and partial ionization cross-sections for CO and N2 in the energy range 18–50 eV

Abstract Branching ratios for photoionization to various ion states of CO and N 2 have been measured in the energy range 18–50 eV using an electron—electron coincidence technique at an ejected electron angle of 90°. The branching ratios, which show a marked variation with energy are shown to be in good agreement with the results of conventional photoelectron spectroscopy at those energies where quantitative PES measurements have been made. The results indicate that the effect of the assymmetry parameter, β, is relatively insignificant in the case of CO and N 2 . Partial oscillator strengths have been determined from the branching ratios using recent total photoabsorption data. In addition to the expected one electron ion states, others are observed arising from two electron processes and the variation of these cross-sections with energy loss is also reported.

An (e,2e) study of ammonia: Binding energies and momentum distributions of valence electrons

Abstract The valence shell electronic structure of NH 3 is studied in an (e,2e) experiment with symmetric non-coplanar geometry. The momentum distributions obtained for the separate orbitals are compared with those calculated from several approximate wavefunctions. The 3a 1 distribution is found to be particularly sensitive to the form of the wavefunction.

Branching ratios and partial oscillator strengths for the photoionization of NH3 in the 15–50 eV region

Abstract The branching ratios for dipole ionization from the three valence orbitals of NH 3 have been determined up to 50 eV using an improved electron impac

Partial oscillator strengths (25–50 eV) of the one-electron states of CH4+, measured in an (e, 2e) experiment

Abstract An (e, 2e) experiment (quantitatively simulating photoelectron spectroscopy) with forward scattering of the fast (3.5 keV) projectile and detection of ejected electrons at the magic angle (54.7 3 ), has been performed on CH 4 . The partial oscillator strengths of the (1t 2 ) −1 and (2a 1 ) −1 states of the ion over the energy range of 25–50 eV are found to be in good agreement with earlier results of a complementary electron-ion coincidence experiment. Higher states due to two-electron transitions are observed to have ionisation potentials of ≈28 ans 31 eV. Branching ratios for these states are given at 35 and 40 eV.

Molecular orbital momentum distributions and binding energies for H2O using an electron impact coincidence spectrometer

Abstract The construction and operation of an instrument which uses the techniques of coincidence counting and electron impact spectroscopy is reported for the study of molecular ionization at large momentum transfer in which the two outgoing electrons are detected at 45° to the incident beam. Variation of the incident energy provides binding-energy spectra for Xe, CH 4 and H 2 O up to 45 eV. Alternatively variation of the azimuthal angle (symmetric, non-coplanar geometry) gives a measure of the electron momentum distribution for any selected orbital in the binding-energy spectrum. Momentum distributions for the four valence orbitals of H 2 O are compared with various wavefunctions from the literature.

The assignment of the ionization potentials of formaldehyde by an (e, 2e) experiment

Abstract The angular variation of the binding energy spectrum in an electron-electron coincidence experiment indicates that the third and fourth ionization potentials of formaldehyde are due to the 5a 1 and 1b 2 orbitals respectively. The vertical ionization potentials of the 4a 1 and 5a 1 orbitals are found to be 21.15 ± 0.15 and 34.2 ± 0.2 eV respectively.

A kinematic and experimental investigation of the (e,2e) simulation of photoelectron spectroscopy

A general expression has been derived for the coincidence intensity in (e,2e) scattering experiments at small momentum transfers. The relationship with photoelectron spectroscopy using both polarized and unpolarized radiation is discussed. The predictions of the expression have been tested using a rotatable analyser which allows measurements to be made at ejection angles of 54.7 degrees and 90 degrees . Measurements at 54.7 degrees on He, Ne and Ar verify the most significant result of the analysis, namely the existence of a magic angle at which the coincidence intensity is independent of the angular anisotropy factor beta . At an ejected angle of 90 degrees the predicted beta dependence is observed for helium. The expected independence from beta of the coincidence intensity at 90 degrees and an energy loss of 22 eV is checked by comparing branching ratios for ionization of N2 and CO with photoelectron data.

Electron spectroscopy using excited atoms and photons V. Penning ionization of water, alcohols and ethers

Abstract The Penning electron spectra of water, methanol, ethanol, isopropyl alcohol, tertiary butyl alcohol, dimethyl ether, ethylene oxide, diethyl ether, tetrahydrofuran and 1,4 dioxane, obtained using helium metastable atoms (21S, 23S), are compared to their respective photoelectron spectra at 584 A. An analysis of the Penning electron band shape and the position of the peak maximum for the ground state ions suggest significant changes in the Franck—Condon factors in comparison with photoelectron spectra. This may be ascribed to modifications of the target potential energy curves. It is also observed that the relative populations of the ionic states differ appreciably for Penning ionization and photoionization.

A study of the bonding in phosphine by an electron impact coincidence experiment

Abstract The binding-energy spectrum of phosphine has been obtained over the range 0–30 eV using the binary (e, 2e) coincidence method. The momentum distribut