D. L. Hansen

THE K-SHELL AUGER DECAY OF ATOMIC OXYGEN

Relative photoionization cross sections for and produced by the Auger decay of a 1s hole in atomic oxygen were measured by using synchrotron radiation between 525 and 553 eV. Energies and quantum defects of the members of the two Rydberg series converging to and ionization thresholds were determined. In addition, the and ionization thresholds were calculated from the two Rydberg series. The 182 meV resolution of the monochromator allowed a detailed study over both thresholds revealing evidence for post-collision interaction and allowing a comparison of the ionization continuum above both and thresholds with that of the ionization continuum above the Ar edges. This comparison indicates that the lifetimes of the Ar(2p) and O(1s) hole states are approximately the same.

Beyond the dipole approximation: angular-distribution effects in valence photoemission

Angular distributions of valence photoelectrons showing effects due to higher-multipole photon interactions have been measured for the first time. Neon 2s and 2p photoemission exhibits effects beyond the dipole approximation throughout the 250 - 1200 eV photon-energy range studied. The results suggest that any photoemission experiment, on any sample, can be affected at relatively low photon energies, pointing to a general need for caution in interpreting angle-resolved-photoemission measurements.

Photofragmentation of third-row hydrides following photoexcitation at deep-core levels

The relaxation dynamics of HCl, DCl, H2S, and D2S following photoexcitation in the vicinities of the Cl and S K-shell thresholds ( ;2.8 keV for Cl, ;2.5 keV for S! were studied by means of ion time-of-flight mass spectroscopy. In all cases, the onset of pre-edge core-shell photoionization precedes the formation on resonance of a significant amount of neutral hydrogen as well as postcollision-interaction effects above threshold. Examination of the width of the H 1 peak in spectra taken with the analyzer parallel and perpendicular to the polarization vector of the incident light indicates that on resonance, the photofragmentation asymmetry parameter, b, is approximately two for HCl, and is clearly positive for H2S. @S1050-2947~98!08211-0# PACS number~s!: 33.80.Gj, 33.80.Eh Time-of-flight mass spectroscopy and coincidence measurements of atoms and molecules are relatively wellunderstood techniques @1‐3#. Coupled with the high bright

Multi-ion coincidence measurements of methyl chloride following photofragmentation near the chlorine K-edge

Relaxation dynamics of CH3Cl following core-shell photoexcitation in the neighbourhood of the chlorine K-edge ( 2.8 keV) were studied via multi-ion coincidence measurements using a time-of-flight mass spectrometer. The data provide evidence for sequential fragmentation moderated by Coulombic interactions among the fragments. The sequential nature of the fragmentation indicates that chemical forces, especially between the carbon and chlorine atoms, are dominant in determining the kinematics of the fragmentation. This is especially true on resonance where fast dissociation is observed following electron excitations to the 8a1 antibonding orbital.