Vibrations of acrylonitrile in N1sexcited states

Abstract

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 ${\ensuremath{\pi}}^{\ensuremath{\ast}}$-orbital localization and hybridization on vibrations accompanying core excitation is discussed. Transition to the ${\ensuremath{\pi}}_{\ensuremath{\perp}}^{\ensuremath{\ast}}(\text{C}=\text{C}\ensuremath{-}\text{C}\ensuremath{\equiv}\text{N})$ delocalized orbital excites mostly stretching vibrations of the whole spinal column of the molecule. Promoting a core electron to the localized ${\ensuremath{\pi}}_{\ensuremath{\parallel}}^{\ensuremath{\ast}}(\text{C}\ensuremath{\equiv}\text{N})$ produces $\text{C}\ensuremath{\equiv}\text{N}$ stretching vibration combined with two strong bending modes of the $\text{C}\ensuremath{-}\text{C}\ensuremath{\equiv}\text{N}$ end of the molecule, related to the change of carbon hybridization.