E. Kukk

Adiabatic and vertical carbon 1s ionization energies in representative small molecules

Abstract Adiabatic and vertical carbon 1s ionization energies are reported for methane (CH 4 ), ethane (CH 3 CH 3 ), ethene (CH 2 CH 2 ), ethyne (HCCH), carbon monoxide (CO), carbon dioxide (CO 2 ), fluoromethane (CH 3 F), trifluoromethane (CHF 3 ), and tetrafluoromethane (CF 4 ) with an absolute accuracy of about 0.03 eV. The results are in good agreement with earlier values but are measured with higher resolution and accuracy than has previously been available.

Carbon 1s photoelectron spectroscopy of CF4 and CO: Search for chemical effects on the carbon 1s hole-state lifetime

Carbon 1s photoelectron spectra for CF4 and CO have been measured at several photon energies near the carbon 1s threshold. The spectra have been analyzed in terms of the vibrational structure and the natural linewidth. For CO the vibrational structure shows evidence for anharmonicity in both the energy spacing and the intensity. Analysis of the results using an anharmonic model gives an equilibrium bond length for core-ionized CO that is 4.85 pm shorter than that of neutral CO. For CF4, the vibrational structure is very weak, and the analysis shows that the change in equilibrium CF bond length upon ionization is no more than 0.54 pm. Ab initio theoretical calculations give results in accord with these bond-length changes. The unusually small bond-length contraction in CF4 can be understood in terms of nonbonded fluorine–fluorine repulsion. The natural linewidth for core-ionized CO, 95±5 meV, is essentially the same as that of CH4. This result is in contrast with expectations based on the one-center model ...

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.

Xenon N4, 500 Auger spectrum - a useful calibration source

Abstract In the xenon N 4,5 OO Auger spectrum there are 19 prominent lines ranging in kinetic energy from 8 to 36 eV that provide a convenient set of standards for calibrating electron spectrometers. Combining optical data with recent measurements of this spectrum gives energies for these lines that are absolutely accurate to 11 meV. For most lines the relative accuracy is better than 1 meV; for a few it is about 3 meV. The spin–orbit splitting of the xenon 4d lines is determined to be 1979.0±0.5 meV.

Partial Auger decay rates of core-ionized molecular states in HCl and DCl

The Cl 2p ionization and the subsequent 2p-1 to 2 pi -2 Auger decay in HCl and DCl molecules have been studied using synchrotron radiation. The Auger spectra have been decomposed and assigned to the transitions from the 2 Pi 1/2, 2 Sigma 1/2 and 2 Pi 3/2 molecular states of the 2p core hole configuration. The 2 Sigma 1/2 and 2 Pi 3/2 states have been found to be separated by 79(8) meV (HCl) and 83(8) meV (DCl). The partial Auger decay rates from different core ionized states have been shown to differ considerably.

Carbon 1s photoelectron spectroscopy of six-membered cyclic hydrocarbons

The carbon 1s photoelectron spectra of cyclohexane, cyclohexene, 1,3-cyclohexadiene, and 1,4-cyclohexadiene have been measured. These have been analyzed in terms of a theoretical model of the vibronic structure that includes the effects of the changes in equilibrium geometry that accompany core ionization as well as those of vibronic coupling in the core-ionized molecule. This theoretical approach gives an excellent description of the vibronic structure and makes it possible to identify the contributions of the inequivalent carbon atoms to the spectra. The carbon 1s ionization energies are reported and used in the analysis of photoelectron spectra of adsorbed molecules.

N-K near edge x-ray absorption fine structures of acetonitrile in gas phase

The dynamic processes of N(1s) core-hole excitation in gas-phase CH3CN molecule have been studied at both Hartree-Fock and hybrid density-functional theory levels. The vibrational structure is analyzed for fully optimized core-excited states. Frank-Condon factors are obtained using the linear coupling model for various potential surfaces. It is found that the vibrational profile of the N-K absorption can be largely described by a summation of two vibrational progressions: a structure-rich profile of nu(CN) stretching mode and a large envelope of congestioned vibrational levels related to the strong (-C-CN) terminal bending bond. Excellent agreement between theoretical and experimental spectra is obtained.

Soft x-ray ionization induced fragmentation of glycine

X-ray absorption commonly involves dissociative core ionization producing not only momentum correlated charged fragments but also low- and high-energy electrons capable of inducing damage in living tissue. This gives a natural motivation for studying the core ionization induced fragmentation processes in biologically important molecules such as amino acids. Here the fragmentation of amino acid glycine following carbon 1s core ionization has been studied. Using photoelectron-photoion-photoion coincidence technique, a detailed analysis on fragmentation of the sample molecule into pairs of momentum correlated cations has been carried out. The main characteristics of core ionization induced fragmentation of glycine were found to be the rupture of the C-Cα bond and the presence of the CNH(2)(+) fragment.

Limitations of the ionic model in describing core-hole decay: molecular versus crystalline KCl

Normal Auger decay spectra of the 2p core hole in potassium have been measured both for molecular gas-phase and crystalline solid-state samples of KCl. While the spectrum for the latter is easily interpreted using a strictly ionic approach, the molecular spectrum gives evidence of strong additional effects. The observed differences between the two phases are discussed from the viewpoint of the ionic model, considering also the perturbation by the different environments and symmetries. The uniquely molecular effects seen in the Auger electron spectra are attributed to the sudden change in character of the valence (Cl 3p) orbital upon core-hole decay, accompanied by dynamic relaxation processes.

Line shape and lifetime in argon 2p electron spectroscopy

Abstract The argon 2p photoelectron spectrum and the argon L3M23M23 1S0 Auger spectrum have been measured at several photon energies between 6 and 80 eV above the 2p3/2 threshold with an instrumental line width significantly smaller then the natural line width. The spectra are described well by the theory of van der Straten et al. [Z. Phys. D 8 (1988) 35] provided that allowance is made for the instrumental resolution and measurements are made at a sufficiently low pressure. The lifetime (Lorentzian) line width determined from these measurements for the core-ionized atom is 112±3 meV, in good agreement with the line width for the 2p3/2→4s core-excited state, 114±2 meV, indicating that the 4s electron has little influence on the Auger decay rate. Remeasurement of the line width for the carbon 1s hole in carbon dioxide gives values in good agreement with the previous measurement of 99 meV.