Patrick Gerard

Photoelectron dynamics of the valence shells of benzene as a function of photon energy

Angle‐resolved photoelectron spectroscopy was carried out on the first nine valence orbitals of benzene using synchrotron radiation as a photon source. From these data cross sections σ and angular distribution parameters β were obtained over a photon energy of 10 to 34 eV. The experimental results are compared with calculations for the same parameters, based on the multiple scattering Xα method. Considering the complexity of the molecule, the comparison is gratifying. A number of shape resonances, which are predicted, have been identified experimentally. The orbital assignments for the photoelectron spectrum of benzene have been reexamined in view of the cross sections and angular distributions and have for the most part been verified.

Photoelectron dynamics of the Cooper minimum in free molecules

The general properties of the Cooper minimum in molecules are reviewed. Experimental results from synchrotron radiation together with theoretical calculations are presented on both the partial cross sections and angular distribution parameters, β. A detailed examination of HCl is used as an example. Previously unpublished results on CClnH4−n, CClnF4−n, ethylene dichloride, I2 and ICl are included. The Cooper minimum is largely discussed as a perturbation from atomic behavior, and is examined as a function of atomic number. The Cooper minimum is also examined as a function of chemical environment. Finally, needs for future research are briefly described.

Autoionization between the ionization thresholds for the 2Π3/2 and 2Π1/2 states of HI+

Angle‐resolved photoelectron spectroscopy was carried out on hydrogen iodide using synchrotron radiation. Applying the constant ionic state (CIS) method, studies were made on resonances associated with autoionization between the ionization potential for the two spin‐orbit split lone pair orbitals, π3/2 and π1/2. Data on both partial cross sections and angular distribution parameters, β, were obtained for the production of the first ionic state 2Π3/2 (v=0). These data indicate the presence of several series of Rydberg states leading to the second ionization potential 2Π1/2 (v=0). Both broad and sharp resonances were observed. A detailed comparison of the data is made with a MQDT calculation in the range of 10.6 to 10.73 eV. Although theory predicts some of the features correctly, there is much room for improvement. Results on the first excited vibrational state [2Π3/2 (v=1)] are also presented and the effects of vibrational states are discussed.

Resonant auger processes for molecules as studied with angle resolved electron spectrometry

Abstract Auger electron spectra of gaseous molecules arising from resonances that occur just below the core shell ionization potential have been measured using a variable photon source from synchrotron radiation. The systems studied include excitation from the 2 p subshells of silicon, sulfur and chlorine for SiCl 4 , CS 2 , COS, CCl 4 , CHCl 3 ), CH 2 Cl 2 and CH 3 Cl. Simultaneous measurement of ejected electrons in both the direction of the polarization vector of the light source and perpendicularly to it have been used to assist in the deconvolution of the photoelectron spectrum of the valence orbitals from the Auger spectrum. It is found in most instances that following resonant absorption, the excited electron acts as a spectator in the Auger decay, although an instance of direct participation of the excited electron is given in the case of SiCl 4 . A simple model based on spectator electron processes is discussed for correlating data on the kinetic energy of the Auger electrons with the resonance energy. Angular distribution parameters, β, have been obtained for the principal peak in the Auger spectrum as a function of photon energy for each of the molecules. The results indicate a rather flat response with β close to zero except for a slight rise at lower energies. Observations, including those on angular dependence, were also made on more highly resolved Auger spectra. The importance of multiplet splitting is discussed. An overview of the area of research on resonance Auger processes is given with suggestions for future research.

Autoionization from the lone‐pair orbitals of molecules containing iodine

Autoionization to the lowest spin component of the ground state of the ion has been studied for the following alkyl iodides in the gas phase: CH3I, C2H5I, and nC3H7I. Measurements have been made using the constant ionic state (CIS) method for photon energies between the ionization potentials arising from the spin–orbit split lone‐pair orbitals of iodine. To carry out the measurements, angle resolved photoelectron spectrometry has been coupled with a variable photon source extracted from synchrotron radiation. A series of broad resonances together with some sharp resonances are seen for each study and the results for each molecule in the series show strong similarity to one another, illustrating the localized atom‐like character of the lone‐pair orbital. There are strong differences found in the extent of the background, which is attributed to the higher density of states for the longer carbon chains. Most measurements were taken for the ground state vibrational level, but results are also presented for ionization to the ν2 excited vibrational state of CH3I+. New resonances, not seen for the ground vibrational state, are found and their origin discussed. CIS spectra on the I2 molecule are reported, which are in strong contrast to the alkyl iodides. Possible reasons for the differences are presented.

Photoelectron study of the 4d subshell of atomic tin between 35 and 115 eV

Partial cross sections σ and angular distribution parameters β have been measured for the 4d electrons of atomic tin between 35 and 115 eV. Our data for tin (Z=50) are compared with relativistic-random phase approximation (RRPA) calculations on the closed-shell atom cadmium (Z=48). Satisfactory agreement is found if the results are normalized to the same photoelectron energy. Comparison with RRPA calculations made for palladium (Z=46) and xenon (Z=54) reveals some differences. Other experimental data for the β parameter are in good agreement with our values.