Intensity analysis of the torsional spectrum of CH3CH3

The far-infrared spectrum of gaseous CH3CH3 has been measured in the region of the torsional fundamental under relatively large pressure-path length conditions. Observations were made at resolutions of 0.08, 0.02, and 0.016 cm−1 and under various experimental conditions using two different Fourier transform spectrometers. In addition, a very high resolution (0.0014 cm−1) spectrum of the lowest lying degenerate fundamental ν9 was obtained. From a frequency analysis of the far-infrared spectrum and 737 lower state combination differences in ν9 and its associated hot band ν9+ν4−ν4, an improved set of torsion–rotation parameters was obtained. An intensity analysis of the torsional bands was carried out to obtain torsional dipole moments. The torsional dipole components μ⊥ and (μ∥−μ⊥ ) were determined to be 9.37(70) and −31.7(2.0) μD, respectively. These experimental values are in good agreement with calculated values of μ⊥=10.13 μD and (μ∥−μ⊥ )=−35.10 μD. The shape of the torsional bands can be reproduced in detail with the model adopted here.