Effect of temperature on the infrared band shapes and reorientational and vibrational relaxation of liquid acetonitrile

Abstract

Infrared band shapes of the CH stretching ν 1 and the CC stretching ν 4 vibrations have been measured at various temperatures in the −41–70°C range. The band widths of the fundamental transitions were obtained by resolving the band overlap with hot band transitions and other modes by least-squares fitting with a computer. The reorientational and vibrational relaxation times were obtained by plotting the band widths against the absolute temperature divided by the viscosity. The reorientational relaxation times obtained from the ν 1, ν 4 and previously studied ν 2 band widths are in beautiful agreement with each other and consistent with the previous results by the Raman and NMR methods. To our knowledge, this is the first to obtain the consistent results for the molecular reorientation from different infrared bands without using the Raman results. The vibrational relaxation times for the ν 2 and ν 4 bands are consistent with the previous Raman results, but, for the ν 1 band, the infrared result is at least 20–30% shorter than the Raman results.