High energy CH-overtone spectra of benzene at 1.8 K

Abstract

It is now well established that the transition energies CH-stretching overtones in large molecules can be fit to the Birge-Sponer relationship [1]. The description of the bandwidths of the transitions, however, has not been as clearly ascertained. Previous experimental work has determined the homogeneous braodening (from Lorentzian line shape fits) of the CH-stretch overtones of benzene [2] and naphthalene [3] in the gas phase and low-tempertature (2 K) crystals, respectively. In a subsequent study [4] of durene (tetramethylbenzene) at low temperature (~2 K), a rather large difference in the bandwidths of methyl bands (25 cm^-1) compared to the aromatic band (~100 cm^-1) at Δν = 5 was found. The contributions of energy and phase relaxation to the homogeneous broadening have been discussed recently [4]. At room temperature, both types of bands are rather broad (~200 cm^-1) and approach the linewidth usually observed for liquids which have a significant congestion due to, e.g., librational sequence progressions [5].