The CS molecule has been studied with constant ionic state (CIS) spectroscopy in the photon energy range 11.2–19.5 eV using radiation from a synchrotron source. The spectra were obtained by monitoring the intensities of the first three vibrational components in the first photoelectron band as a function of photon energy. The structured spectra obtained have been analyzed in terms of excitation to and autoionization from Rydberg states with A 2Π, B 2Σ+, and C 2Σ+ ionic cores. Photoelectron spectra of the first band of CS recorded at selected resonant energies showed extended vibrational structure which was used to obtain improved ionic state vibrational constants for CS+ X 2Σ+ compared to those derived from an off-resonance spectrum.

The atmospherically important species O-2(a (1)Delta(g)) has been studied by photoelectron spectroscopy using vacuum ultraviolet radiation from a synchrotron as the photon source. Constant-ionic-state (CIS) spectra, recorded for vibrational levels of O-2(+)(X (IIg)-I-2,) nu(+)=0,1,2,3 accessed from O-2(a (1)Delta(g)) nu "=0, exhibit intense signals in the photon energy region 14.0-15.5 eV which are shown to arise from autoionization from a Rydberg state with an O-2(+)(C (2)Phi(u)) core. On the basis of the results obtained and earlier evidence derived from vacuum ultraviolet absorption spectroscopy, this state is assigned as a (C (2)Phi(u), 3s sigma(g)) (1)Phi(u) Rydberg state. Photoelectron spectra recorded for O-2(a (1)Delta(g)) at positions of strong resonances have allowed extended vibrational structure to be obtained in the first photoelectron band. The relative vibrational component intensities in the resonant photoelectron spectra are in good agreement with computed relative intensities obtained via Franck-Condon calculations, confirming the vibrational numbering of the resonances in the (1)Phi(u) state. Competition between autoionization and predissociation in the (1)Phi(u) Rydberg state is discussed on the basis of the results obtained. Weaker structure is observed in CIS spectra recorded in the photon energy regions 12.5-13.5 and 15.0-20.0 eV. Suggestions are made for the nature of the highly excited states of O-2 associated with this structure, based on available ionization energies and spectroscopic constants of known ionic states accessible from O-2(a (1)Delta(g)). For example, two broad bands centered at approximate to 16.4 and approximate to 17.75 eV are assigned to excitation to Rydberg states arising from the configurations (D (2)Delta(g), 3p pi(u)) and (D (2)Delta(g), 4p pi(u)) respectively. (C) 1998 American Institute of Physics.

The SO molecule has been studied by photoelectron spectroscopy using vacuum ultraviolet radiation from a synchrotron as the photon source. Both constant ionic state (CIS) and photoelectron spectra have been recorded. Resonances which appear in the CIS spectra recorded for selected vibrational levels of SO+ X 2Π in the photon energy region hν=11.5–15.0 eV have been assigned to excitations to Rydberg states which converge to the SO+ a 4Π and A 2Π states and autoionize to SO+ X 2Π. Also, resonances which appear in the CIS spectra recorded in the photon energy region 15.0–16.4 eV for selected vibrational levels of SO+ b 4Σ− have been assigned to excitations to Rydberg states which converge to SO+ B 2Σ− and autoionize to SO+ b 4Σ−. Photoelectron spectra recorded at selected resonant photon wavelengths show that autoionization can dramatically alter the intensities of the vibrational components in a photoelectron band and may allow extra vibrational structure to be observed. The additional information obtained from using this method to study short-lived molecules is discussed.

The gas-phase He(I) photoelectron spectra of the MF4(M=Ti, Zr, Hf) molecules have been recorded for the first time. Assignment of the spectra was achieved with the aid of ab initio molecular orbital and density functional theory (DFT) calculations. The spectra are found to be similar for each molecule, with the exception that the A2T2 ionic state in HfF4 is split by spin–orbit interaction. The measured splitting (0.18±0.03) eV, is in very good agreement with the value obtained from a relativistic DFT calculation, 0.16 eV, and arises from a small contribution from the Hf 5p orbital into the upper t2 molecular orbital of HfF4.

Constant ionic state (CIS) and photoelectron spectra have been recorded for the SO(X3∑−) molecule using a photoelectron spectrometer specifically designed for the study of short-lived molecules in the gasphase with synchrotron radiation.