J.W. Taylor

Angle-resolved photoelectron spectroscopy of the chloro-substituted methanes☆

Abstract The angular distribution parameter, β, was determined for the valence orbitals (IP ′ 21.2 eV) of CCl4, CHCl3, CH2Cl2, and CH3Cl in the 10–30 eV photon energy range using dispersed polarized synchrotron radiation. The energy dependence of β in the photoelectron energy range of 2 to 10 eV for the non-bonding chlorine n(Cl) orbitals of these molecules was found to be similar for all n(Cl) orbitals investigated. The energy dependence of β for the σ orbitals in these molecules was similar to that observed previously for other σ orbitals. The experimental CCl4 results were compared with theoretical CCl4 results obtained using the Xα multiple scattering formalism. Theory predicts the existence of two strong shape resonances in each of the valence orbitals of CCl4. The overall agreement between experiment and theory is evaluated along with the experimental evidence concerning the verification of the predicted shape resonances.

Angle-resolved photoelectron spectroscopy of formaldehyde and methanol☆

Abstract Angle-resolved photoelectron spectroscopy was employed to obtain the angular distribution parameter, β, for the valence orbitals (IP

Angle-resolved photoelectron measurements on the 2p orbitals of Si in SiF4 and Si(CH3)4 in the gas phase

Abstract Angle-resolved photoelectron measurements have been carried out on the 2p orbital of Si in the gas-phase molecules SiF 4 and Si(CH 3 ) 4 as a function of energy from 3 to 45 eV above the ionization threshold. From these data the angular distribution parameter, β, has been obtained. Below a photoelectron energy of 15 eV the angular distribution parameter for these two molecules differ by as much as 0.4 units. The differences in the behavior of β near threshold for the two molecules is attributed to the different molecular environment of the silicon atom. To test this idea, calculations have been made on β for neutral and charged atomic silicon.

A systematic angle-resolved photoelectron study of π orbitals in unsaturated organic molecules

Abstract The angular distribution parameter β has been determined for the π orbitals of 1,1-dichloroethylene, tetrachloroethylene, tetrafluoroethylene, propylene, 1-butene, isobutylene, cis-2-butene, trans-2-butene, 1,3-butadiene, cyclopentene, methylacetylene and furan in the photon energy range 10–30 eV using dispersed polarized synchrotron radiation. The energy dependence of β in the photoelectron energy range 2–10 eV was found to be similar for all the π orbitais investigated. The potential use of the energy dependence of β as an aid in making molecular-orbital assignments is discussed. Resonance photoionization features similar to those observed for the π orbitals of acetylene, ethylene and benzene were found in many of the π orbitals of the molecules investigated herein. Possible explanations for these resonance features are discussed.

Angle-resolved photoelectron spectroscopy of cyclopropane☆

The angular distribution parameter, β, determined for the valence orbitals (IP < 18 eV) of cyclopropane in the 10–30 eV photon energy range using dispersed polarized synchrotron radiation. The energy dependence of β for photoelectron energies between, 2 and 10 eV above threshold was found to be similar to those found previously for other σ orbitals. The effects of Jahn-Teller splitting on β for the 3e′ orbital were found to be small but definitely present. The overall shape and magnitude of the β(hv) curve are, however, sufficiently for the different Jahn-Teller components that, for purposes of orbital assignments using β(hv) curves the shape and magnitude of the curves can be considered associated only with the initial state. Resonance photoionization features at a photon ener of ≈ 18 eV were observed in the 3e′ and 3a′1 orbitals and tentatively assigned to autoionization.

Absolute partial photoionization cross sections of ethylene

Abstract Absolute partial photoionization cross sections for ionization out of the first four valence orbitals to the X 2 B 3u , A 2 B 3g , B 2 A g and C 2 B 2u states of the C 2 H 4 + ion are presented as a function of photon energy over the energy range from 12 to 26 eV. The experimental results have been compared to previously published relative partial cross sections for the first two bands at 18, 21 and 24 eV. Comparison of the experimental data with continuum multiple scattering Xα calculations provides evidence for extensive autoionization to the X 2 B 3u state and confirms the predicted shape resonances in ionization to the A 2 B 3g and B 2 A g states. Identification of possible transitions for the autoionizing resonances have been made using multiple scattering transition state calculations on Rydberg excited states.

Recent Developments in Photoelectron Dynamics Using Synchrotron Radiation

Through a collaborative effort of members of the Oak Ridge National Laboratory and Universities of Wisconsin and Tennessee, a comprehensive study of atoms and molecules using angle-resolved photoelectron spectroscopy and synchrotron radiation is underway at the Synchrotron Radiation Center, Stoughton, Wisconsin. Over 50 molecules and atoms have been investigated. These results, coupled with theory, aim at a better understanding of the dynamics of photoionization and of the wave functions that control these processes. In particular, attention is given to the following topics: metal atomic vapors, generalization of molecular orbital types, autoionization, shape resonances, core shell effects, satellite structure and the Cooper minimum.

Relative partial photoionization cross-section of methylacetylene to the X2E ion state over the photon energy range 11–26 eV

Abstract Relative partial cross-sections for photoionization to the X 2 E ground state of the methylacetylene ion over the photon energy range 11–26 e V have been determined using synchrotron radiation. The observed cross-sections show a broad resonance feature similar to the results for photoionization to the X 2 II u ground state of the acetylene ion. An explanation involving autoionization from a π * (e) excited state is proposed.

Angle-resolved photoelectron study of the group VIB metal hexacarbonyls M(CO)6 (M=Cr, Mo, W) from 9 to 30 eV photon energy

Abstract Theoretical MS Xα angular distribution parameters β have been calculated from 9 to 30 eV in photon energy for the metal hexacarbonyls M(CO) 6 (M=Cr, Mo, W). The theoretical results for the n t 2g −1 ( n =2 (Cr), 3 (Mo), 4 (W)) d-orbital bands are discussed and compared to experimental measurements obtained using gas-phase photoelectron spectroscopy. Evidence for shape resonances at ≈ 3.0 and ≈ 5.5 eV kinetic energy above threshold in the ϵe u and ϵt 1u channels, respectively, for each of these compounds is presented. The nature of these resonances is discussed and compared to other polyatomic systems.

Parity-unfavored transitions in resonant photoemission from Ar, Kr, and Xe: experimental and theoretical results

Abstract High-resolution angle-resolved electron spectroscopy with synchrotron radiation has been used to study the angular distributions of resonant-Auger processes near the core-level thresholds Ar2p, Kr3d and Xe4d. Angular-distribution parameters (β) were measured for all resolved peak in the electron spectra and large negative values of β were found for some peaks. A quantitative method for calculating the angular-distribution parameters is described and results of calculations for the Ar2p 3 2 →4s resonant-Auger spectrum are compared with the experimental results.