S. J. Osborne

The vibrationally resolved C 1s core photoelectron spectra of methane and ethane

Recent progress in the development of high-resolution electron spectrometers in combination with highly monochromatized undulator radiation has allowed observation of the vibrationally resolved gas-phase C 1s photoelectron spectra of methane and ethane. For both molecules, the C–H stretching modes are well resolved and for ethane the active C–C stretching mode has been observed for the first time. The spectra have been measured at low kinetic energies and detailed fittings using post-collision interaction line profiles have been made both, using a free parameter fit and a fit adhering to a linear coupling model. The free parameter fit allows for any anharmonicity in the vibrational energies. The linear coupling model, on the other hand, assumes that the initial and final state potential curves are harmonic and differ only in the normal coordinates. This simple model is used to reduce the number of free parameters in the fit, which greatly simplifies the analysis. An intensity model based on the linear cou...

The vibrationally resolved participator Auger spectra of selectively excited C 1s(2σ)−12π1 vibrational states in carbon monoxide

The fully vibrationally resolved participator Auger spectra originating from the decay of the C 1s(2σ)−12π1 resonance in CO are presented. The C 1s(2σ)−12π1 v’=0 resonance has been excited with a 75 meV monochromator bandpass, i.e., in Auger resonant Raman conditions, and the participator Auger spectrum observed. The C 1s(2σ)−12π1 v’=1 resonance is also excited and the corresponding participator Auger spectrum observed with a monochromator bandpass slightly larger than the inherent width. The results are compared to theoretical simulations using coherent lifetime‐vibrational interference theory which accounts for the details of the spectrum. We have observed an interference shift on the transitions to different vibrational sublevels in the final state. A high resolution C 1s photoelectron spectrum of CO is also presented. The lifetime width of the C 1s core–hole state is determined to be 97(10) meV, whereas the C 1s(2σ)−12π1 resonance is measured to have a width of 86(10) meV.

High-resolution study of the correlation satellites in photoelectron spectra of the rare gases

Abstract High-resolution, synchrotron radiation excited valence photoelectron satellite spectra, taken at the magic angle, of all the rare gases, He, Ne, Ar, Kr and Xe, are presented. The facilities at the Finnish beam line at the MAX laboratory have been used to extend the resolution and energy regions as compared to previous measurements at comparable excitation energies around 100 eV. Comparisons of the results are made with optical data, with previous synchrotron radiation studies, and with low- and high-excitation energy results from conventional radiation sources. A very large number of new spectral features have been observed. In particular, the asymmetric Fano line profile of several satellite lines has been revealed.

Auger decay of the dissociating core‐excited states in the HCl and DCl molecules

High‐resolution Auger electron spectra from the decay of the Cl 2p→σ* excitation in HCl and DCl have been measured. The spectra are analyzed, separating molecular and atomic features, which are assigned to transitions to the HCl (5σ2π)4σ* and Cl (3s3p)6 states, respectively. Auger line shapes, as affected by the molecular dissociation, are studied by comparing the experiment with the results of Monte‐Carlo computer simulations based on a semiclassical model.

Auger decay of the molecular field split S 2p core excited states in HS radical

Using synchrotron radiation, very high resolution electron spectra at the 2p→6a1 and 2p→3b2 resonances of H2S have been recorded. Auger transitions from molecular field split S 2p hole states of HS* fragment, created by fast dissociation of the core excited H2S, are found to reveal different partial rates depending on the symmetry of the final state. The experiments have made it possible to determine, for the first time, the molecular field splitting of the core levels in a free radical. The molecular field splitting between the 3σ1/2 and 1π3/2 (“2p3/2’’) levels in the HS* fragment is found to be 90(5) meV, which significantly differs from the molecular field splitting of the “S 2p3/2’’ levels in the H2S molecule. Resonant Auger decay in the molecule before dissociation is also observed.

High-resolution photoelectron satellite spectrum of He excited by synchrotron radiation at 96.5 eV photon energy

The photoelectron spectrum of He has been measured, with very high resolution, using synchrotron radiation at 96.5 eV photon energy. The final Rydberg states in the satellite spectrum can be followed up to n=11. The relative intensities have been determined and it is found that the intensities very accurately follow the n-3 dependence for the higher Rydberg states. Also the intensity (per eV) of the shakeoff continuum near to the threshold, relative to the main 1s single-ionization channel has been measured to be 0.20(2)% of the main 1s peak per eV.

Site-Selective Participator Decay of Core-Excited Butadiene

The decay of core‐excited electronic states in free 1,3 trans butadiene molecules has been studied using high‐resolution synchrotron radiation and electron spectrometry. The core‐level energy shift between the terminal and central carbon atoms is 0.64 eV making selective excitation of core electrons from these atoms possible. Resonant excitation to the au(π*) valence state leads to autoionizing decay channels which proceed according to the atomic site in the molecule. The radiationless decay is localized, and certain molecular orbitals are excluded from the decay depending upon the site of the core hole. This phenomenon is confirmed by semiempirical INDO calculations based upon the equivalent core approximation. The vibrational structure of the resonances below the carbon K edge has been measured and fit to extract vibrational energies and intensities, chemical shifts, and the lifetimes of the centrally and terminally excited states. The C 1s spectrum is also measured with vibrational resolution and the e...

Auger decay of core-excited higher Rydberg states of carbon monoxide

The de-excitation of higher core-excited Rydberg states of carbon monoxide has been studied. It is found that already with a main quantum number of 4 or higher, Rydberg states of p-symmetry can be successfully treated within the single-particle hydrogenic model for both the core-excited and the final states. From a study of the binding energy of the Rydberg electron in the final state versus the core-excited state, the importance of relaxation in the core-excited intermediate state is shown. Also, for core-excited Rydberg states with main quantum number of 5 or higher, an almost total quenching of strict spectator lines in the de-excitation spectra is observed.

Fast dissociation of neutral doubly excited states above the S 2p ionization threshold in H2S

A very rapid dissociation of core doubly excited states in a molecule has been observed for the first time. The channel is identified in the Auger electron spectra of H2S where the resonating structures, at higher kinetic energy than the normal Auger LVV electron lines, display non-dispersive kinetic energies relative to photon energy above the S 2p ionization limits.