T. Gustafsson

The orientation of CO adsorbed on Ni(100)

Abstract We demonstrate the utility of angular resolved photoemission with synchrotron radiation to determine the bonding configuration of adsorbed molecules. This procedure depends on an understanding of the gas phase phase photoexcitation of the molecule and makes specific use of the polarized and continuum nature of the photon source to investigate the angle resolved emission from the adsorbate.

The chemisorption of CO on Cu(100) studied with angle resolved photoelectron spectroscopy

Abstract Using angle resolved UV photoelectron spectroscopy, coupled with the continuum of polarized light available with synchrotron radiation, we make an interpretation of the photoelectron spectrum of CO adsorbed on Cu(100). We point out that the bonding of CO on Cu as observed by photoemission is considerably different from the bonding of CO on Ni. These differences do not seem to be caused by bonding orientation differences, however, as the CO molecular axis is found to be very close to the surface normal, as was the case for CO on Ni(100). No evidence is found for a second phase of CO on Cu(100).

c(2 x 2)CO ON Ni(100): Photoemission orientation determination

Abstract Angular resolved photoemission studies of c(2 x 2)CO adsorbed on Ni(100) show that the molecule is bound to the surface with the molecular axis normal to the surface. The uncertainty of this determination is approximately 15°, which is consistent with the expected angular broadening due to vibrational modes. This is in distinct contrast to a bend of 34° proposed to explain LEED data on this system.

Shape resonances in diatomic molecules: NO

Abstract Photoionization cross sections for the 4σ derived ionic states of NO are reported. Evidence is presented for a σ-type shape resonance 7–8 eV above threshold. The energy position of this resonance is compatible with a simple kinematic scattering model.

Analyzer system capable of determining energy and direction of charged particles in ultrahigh vacuum

We have constructed and tested a system capable of measuring the energy of charged particles emitted from a sample at any angle relative to the sample or the incident beam of exciting particles. The energy analysis is accomplished by a 180 degrees spherical deflecting-type analyzer, operated at constant pass energy with a series of electrostatic lenses. The analyzer system is properly apertured to accept incoming particles from a spot of 1.5 mm diameter at the sample and within a cone of 2.5 degrees half-angle. The lens system used has constant transmission independent of the incident energy. The energy analyzer is independently rotatable about two orthogonal axes, giving it complete freedom of access to any angle of collection relative to the sample orientation. The sample can rotate about two orthogonal axes so that any angle of incidence can be used. Specific examples are given of the performance of the system when used for the measurement of the angular distribution of photoelectrons excited by synchrotron radiation.

Partial photoionization cross sections of molecular oxygen

Abstract Measurements of partial photoionization cross sections of O 2 for excitation energies between 20 and 45 eV are reported and compared to a calculation using the Stieltjes-Tchebycheff moment theory. Positive evidence is obtained for a predicted σ-type shape resonance between 1 and 2 eV above threshold in certain ionic-state cross sections. Implications for angular distribution of photoelectrons from an oriented O 2 are discussed.

Vibrational excitation cross-sections for adsorbed CO

Abstract The energy and angular dependence for inelastic electron scattering from vibrational modes of CO adsorbed on Cu(100) has been investigated. Experimental results for the Cu-CO and C-O stretching vibrational modes are presented and compared with scattering calculations assuming dipole interaction. We find that the characteristic experimental features are in accordance with the predictions of the dipole scattering theory.

Photoionization cross sections of the 5s electrons in Xe measured with synchrotron radiation

Abstract Measurements of the photoionization cross sections of the 5s electrons in Xe between 25 and 40 eV photon-energy using synchrotron radiation are reported. The cross section shows a minimum at 36 ± 2 eV in excellent numerical agreement with a RPAE calculation.