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.