The torsional spectrum of CD3CD3

The perturbation‐allowed torsional spectrum of gaseous CH3CH3 has been measured between 225 and 340 cm−1 at a resolution of 0.015 cm−1 using a Fourier transform spectrometer. The absorption path length was 124 m; the gas temperature and pressure were 295 K and 107 Torr, respectively. The P, Q, and R branches have been observed for all four torsional sublevels in the bands v4=1←0 and 2←1. A torsion–rotation Hamiltonian containing seven parameters was used to analyze 204 frequencies assigned in the P and R branches of the two bands. Effective values were obtained for the reduced rotational constant AR, the two leading coefficients V3 and V6 in the Fourier expansion of the hindering potential, the B rotational constant, and three distortion parameters. Estimates for the three zeroth order torsional parameters free of higher order contributions are: AR =2.6711(50) cm−1, V3=1012.0(1.0) cm−1, and V6=10.71(0.60) cm−1. The torsional energies calculated from the current model are compared to those obtained by earl...