The effect of NH2-inversion tunneling splitting on the NH-stretching overtone spectra of aniline vapour

Abstract

The room temperature vibrational overtone spectrum of aniline vapour has been recorded by intracavity laser photoacoustic spectroscopy in the 9700 cm⁻¹ to 16 600 cm⁻¹ region. The NH-stretching overtone bands exhibit spectral structure due to the tunneling splitting of the amino group inversion states. We find that this tunneling splitting steadily decreases with increasing NH-stretching vibrational excitation, and at the fourth NH-stretching overtone the splitting is negligible. Wave numbers and intensities of the NH- and CH-stretching vibrational overtones were calculated with a harmonically coupled anharmonic oscillator local mode model to facilitate spectral assignment. The conventional liquid phase overtone spectra of aniline were recorded and the measured absolute intensities are in good agreement with the calculated intensities.