High-resolution HeI and HeII excited inner-valence photoelectron spectra of the oxygen molecule have been recorded between 20 and 26 eV. In this range three photoelectron bands are clearly observed that are associated with transitions to the B 'Xg, 'lI", and c X"cationic states. Vibrational structure is observed in all photoelectron bands, and the vibrational constants have been determined. The rotational profile of the vibrational lines is resolved for the B state, and an analysis is made in terms of transitions involving bN =0 and +2. In addition to the three strong bands, a fourth, weak vibrational progression has been observed in the range of the B Xg state. The state of II"symmetry observed around 24 eV shows a long vibrational progression with spacings that decrease successively towards higher electron binding energies. The progression converges at 23.83 eV, slightly below the position where the band has the highest intensity. This II"state is thus shown to be bound with a dissociation energy Do of 2.5 eV.The assignments are confirmed by ab initio calculations, which also provide a vibrational analysis and potential curves that agree very well with the experimental results. These calculations show that the potential curves follow the electron configurations rather than the adiabatic curves in the inner-valence region.
The inner-valence electron states of the methane molecule have been studied by means of x-ray, synchrotron radiation, and UV-photoelectron spectroscopy. Five correlation satellites have been identified and a detailed study has been carried out of the 2a−11 single hole state. For this state a Franck–Condon analysis has been performed, suggesting an equilibrium bond distance of 1.279 Å. The vibrational lines have a Lorentzian shape and the linewidth increases gradually with the vibrational quantum number. This probably indicates a reduction of the lifetime of the vibrational states due to predissociation. A discussion of the potential curves related to the correlation satellites is included.
Extensive modifications of an electrostatic electron spectrometer of the hemispherical type are described. The purpose of the modifications is to make the instrument more suitable for high-resolution gas phase spectroscopy. The changes concern substitution of electrical adjustments for mechanical precision, improved flexibility in focusing, and a new system of computer-controlled power supplies and detector interface. The instrument is also used for energy analysis of positive ions. Conversion between positive and negative particle analysis is achieved simply by reversing the polarities of all relevant voltages by a number of switches. A gas cell with internal heating is described. The influence of gas cell conditions on resolution is briefly discussed. The computer programs used for spectrometer control, data acquisition, spectrometer optimization, and calibration are described.
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