Molecular Bond Length Determination from σ Resonances in Near Edge Spectra

In recent years the K-shell excitation spectra of numerous gas phase molecules containing B, C, N, O and F have been studied by electron energy loss or photoabsorption spectroscopy. A common feature of these spectra is one or more relatively broad peaks in the region of the K-shell ionization threshold. Within a molecular orbital description these features may be attributed to ls → σ* transitions. Alternatively, they may be described as σ shape resonances associated with scattering of the excited core electron by adjacent atoms. The scattering process and in particular, the energy at which the excited electron is trapped by the intramolecular potential, is expected to be a function of the local structure of the core excited atom. We have examined literature molecular K-shell spectra [1] to investigate the relationship between molecular structure and a resonances.