The 3←0 CH stretch overtone of benzene: An optothermal study

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Abstract
The second CH stretch overtone of benzene at the rotational temperature of about 20 K has been measured in a supersonic molecular beam. Infrared absorption has been detected by means of the optothermal method. At least seven vibrational bands have been resolved in the wave numbers range from 8740 to 8870 cm−1. The main absorption peak is located around 8827 cm−1, but a significant absorption is observed also in ‘‘red’’ region of the spectrum, around 8770 cm−1. Experimental spectra have been compared with a theoretical calculation carried out following the method of Sibert et al. [J. Chem. Phys. 81, 1115 (1984)]. No free parameters have been included in the calculation in order to improve the fit with experimental data. Calculations do not provide a detailed quantitative description of experimental data. However the two spectra are qualitatively similar: (a) both are characterized by a main absorption structure located in the 8820–8840 cm−1 region and (b) calculations confirm the experimental observation that a significant part of the CH oscillator strength is borrowed by lines located on the ‘‘red’’ side of the main peak.