Copyright (c) 2012 University of Nevada, Las Vegas All rights reserved. http://digitalcommons.library.unlv.edu Recent documents in University Libraries en-us Tue, 15 May 2012 04:45:06 PDT 3600 http://digitalcommons.library.unlv.edu/hrc_fac_articles/40 http://digitalcommons.library.unlv.edu/hrc_fac_articles/40 Mon, 14 May 2012 19:16:39 PDT 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.

]]> Oliver Hemmers et al. http://digitalcommons.library.unlv.edu/hrc_fac_articles/39 http://digitalcommons.library.unlv.edu/hrc_fac_articles/39 Mon, 14 May 2012 18:33:51 PDT The relaxation dynamics of HCl, DCl, H₂S, and D₂S following photoexcitation in the vicinities of the Cl and S K-shell thresholds (∼2.8keV 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⁺ 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, β, is approximately two for HCl, and is clearly positive for H₂S.

]]> D. Hansen et al. http://digitalcommons.library.unlv.edu/hrc_fac_articles/38 http://digitalcommons.library.unlv.edu/hrc_fac_articles/38 Mon, 14 May 2012 18:05:35 PDT A gas-phase time-of-flight (TOF) apparatus, capable of supporting as many as six electron-TOF analyzers viewing the same interaction region, has been developed to measure energy- and angle-resolved electrons with kinetic energies up to 5 keV. Each analyzer includes a newly designed lens system that can retard electrons to about 2% of their initial kinetic energy without significant loss of transmission; the analyzers can thus achieve a resolving power (E/ΔE) greater than 10⁴ over a wide kinetic-energy range. Such high resolving power is comparable to the photon energy resolution of state-of-the-art synchrotron–radiation beamlines in the soft x-ray range, opening the TOF technique to numerous high-resolution applications. In addition, the angular placement of the analyzers, by design, permits detailed studies of nondipolar angular distribution effects in gas-phase photoemission.

]]> Oliver Hemmers et al. http://digitalcommons.library.unlv.edu/hrc_fac_articles/37 http://digitalcommons.library.unlv.edu/hrc_fac_articles/37 Mon, 14 May 2012 17:00:53 PDT Angle-resolved resonant electron spectra following vibrationally resolved C 1s rightarrow nl lambda (nu= 0, 1) excitations in CO have been measured. The observed groups of resonant Auger lines exhibit great similarity in shape to the C-KVV group of non-resonant Auger lines and the observed angular distribution behaviour reflects the symmetry-dependent anisotropies of the excitation process. The molecular progressions in the C 1s right arrow pi resonant Auger spectrum could be clearly identified due to their different angular distribution behaviour. Furthermore, it could be shown that the screening energies for spectator electrons over binding energy have a linear dependence between 3ppi, 4ppi and threshold as was expected for the higher p-symmetry Rydberg orbitals.

]]> Oliver Hemmers et al. http://digitalcommons.library.unlv.edu/hrc_fac_articles/36 http://digitalcommons.library.unlv.edu/hrc_fac_articles/36 Mon, 14 May 2012 16:38:05 PDT A combined experimental and theoretical study of argon valence photoionization illustrates the discovery of the broad lack of validity of the independent-particle approximation (IPA) for x-ray photoemission. In addition to previously known breakdowns of the IPA, which are limited to high photon energies and regions very near threshold, the observed breakdown in photoionization at intermediate energies demonstrates generally that the IPA is valid only in very restricted domains. These restrictions are expected to be relevant throughout the periodic table, with consequences for a wide variety of applications.

]]> D. Hansen et al. http://digitalcommons.library.unlv.edu/unlv_magazine/22 http://digitalcommons.library.unlv.edu/unlv_magazine/22 Thu, 10 May 2012 17:44:21 PDT Barbara Cloud et al.