Infrared and electronic absorption spectra of n-butyronitrile and its ions using Møller Plesset method.

We report theoretical infrared and electronic absorption spectra of gauche and anti conformers of n-butyronitrile, their ions and 2-methylpropanenitrile isomer of n-butyronitrile. The coupled cluster theory (CCSD) and second order Møller-Plesset perturbation (MP2) theory with TZVP basis set are used for the study. Vibrational frequencies of gauche and anti conformers of neutral n-butyronitrile at MP2/TZVP and CCSD/TZVP levels are in agreement with the experimental determinations. Rotational and distortion constants are also in good agreement with the available experimental values. Time dependent density functional theory is used to study the electronic absorption spectra of gauche and anti conformers, their ions and an isomer of butyronitrile. All the electronic transitions of gauche and anti conformers of neutral n-butyronitrile and 2-methylpropanenitrile are σ→σ* transitions whereas ions of n-butyronitrile show both σ→σ* as well as π→π* transitions in vacuum UV, far UV and visible regions. This study helps in detection of neutral gauche and anti conformer and their ions in interstellar medium.