Amine inversion effects on the IR spectra of aniline in the gas phase and cold inert gas matrixes

Abstract

The mid-infrared spectrum of aniline vapour is reinvestigated, and the IR spectrum of the compound in solid nitrogen matrix under a cryogenic condition is measured for the first time. A thorough assignment of many features of the vapour spectrum, particularly those related to amine inversion mode, is suggested. By use of PGOPHER fitting of the rotational band contours in the fingerprint region, the amine inversion tunnelling splitting at v = 1 level of NH2 scissoring and C–N bending vibrations in the vapour spectrum are identified. Our analysis reveals that excitation of one quantum of NH2 scissoring results in lowering of the tunnelling barrier, whereas, the barrier is increased upon excitation of the C–N bending. Comparison of the spectra recorded in nitrogen and argon matrixes reveal that the former hinders the NH2 inversion and consequently, transitions corresponding to higher quanta of this mode are absent.