Search

The C 1 s −π ∗ band in the high-resolution photoabsorption spectra of the ethyne isotopomers C2H2, C2D2 and C2HD is found to be dominated by vibronic coupling effects. There is quantitative agreement between experiment and a recent theoretical model which treats vibronic coupling in both the core and valence orbital spaces. The theoretical analysis shows that a strong excitation of the bending modes dominates the observed spectra.

We have measured the C 1s near-edge photoabsorption spectrum of the ethene isotopomers C 2 H 4 , C 2 D 4 , (1, 1)C 2 H 2 D 2 and cis-C 2 H 2 D 2 at high resolution using order-sorted, monochromatised undulator radiation. An analysis of the vibrational fine structure on the 1s-π ∗ band indicates strong excitation of non-totally symmetric modes and provides direct evidence for symmetry breaking and core hole localisation.

Lifetime vibrational interference effects modulate the line shapes observed in high-resolution studies of the decay of ultra-short-lived core—hole excited states in molecules. We have analyzed the decay of the 1σ−1u 1π3g core excited state in O2, where for the first time subsets of vibronic eigenfunctions could be selected. We demonstrate that this type of spectroscopy can be used to verify the predictions of quantum mechanical interference theory describing the time evolution of coherently excited vibrational states on the femtosecond time scale.

In an angle-resolved photoelectron study using synchrotron radiation we have re-investigated the C 1s photoionization of CO and CO 2 in the energy region near threshold where the photoabsorption cross sections are characterized by strong shape resonances and transitions to doubly excited states. The much lower scatter in these new data and the extension of the energy range down to 2–3 eV above threshold have made it possible to identify the strong influence of multi-electron excitations on the single-hole partial cross section and the corresponding asymmetry parameter β. Thus, even the single-hole cross section cannot necessarily be used to recover the “one-electron” profile of the shape resonance.