Analysis of Infrared Spectra of Neat Liquid N-Methylpyrrole

The vibrational properties of neat liquid N-methylpyrrole were investigated. Quantitative near-infrared and mid-infrared spectra recordings including thin film MIR transmission studies were performed. Basing on these data the optical constants of N-methylpyrrole in the 12500-560 cm^{-1} region were determined. The experiment was supported by an anharmonic analysis based on Möller-Plesset perturbation theory and density functional theory level of theory, including the hybrid B2PLYP functional. Assignments of numerous bands observed in the liquid phase were proposed basing on potential energy distribution calculations and a comparison of experimental and simulated spectra was presented. The inaccuracy of static calculations in the reproduction of experimental spectrum in the C-H stretching region has been observed and explained by the rotation of methyl group. A vibrational spectrum was therefore calculated by the use of Car-Parinello molecular dynamics method for a better simulation of experimental spectrum.