Vibrations of acrylonitrile in N 1s excited states

The N 1s near edge x-ray absorption fine structure spectra of acrylonitrile gas are accurately reproduced by a complete ab initio multidimensional vibrational analysis. The role of π^∗-orbital localization and hybridization on vibrations accompanying core excitation is discussed. Transition to the π_⊥^∗(C=C−C≡N) delocalized orbital excites mostly stretching vibrations of the whole spinal column of the molecule. Promoting a core electron to the localized π_∥^∗(C≡N) produces C≡N stretching vibration combined with two strong bending modes of the C−C≡N end of the molecule, related to the change of carbon hybridization.