The Infra-Red Spectrum of C2H6

Abstract

The infra-red spectrum of C2H6 gas has been studied in the region between 1.6 and 13μ with a spectrometer of high resolving power. From measurements on four resolved ∥ bands the value IB0 = (42.234±0.011)×10−40 g cm2 has been obtained for the large moment of inertia in the ground state. From measurements on the three fundamental ⊥ bands the best value at present available for the small moment of inertia is IA = 10.81×10−40 g cm2. Because of uncertainties concerning the perturbations of degenerate state ν8, of which a semi-quantitative explanation which is apparently basically correct has been obtained, this value is provisional but appears to be fairly reliable. With these values of IB0 and IA, if one assumes C–C = 1.55A, one obtains C–H = 1.098A and ≰HCC = 109° 3′. From the considerations of the perturbations of state ν8 and of the frequencies and line spacings of the combination ⊥ bands, spectroscopic evidence indicating that the configuration of C2H6 is staggered (point group D3d) has for the first time been obtained. Also from these considerations the reliable value ν8 = 1472.2 cm−1 and the values ν4 = 290 cm−1 for the torsion frequency and ν12 = 1190 cm−1 for the ``uncertain'' frequency have been obtained. The latter two values are perhaps somewhat more reliable and not inconsistent with values obtained previously by other methods. These and other results are summarized in Figs. 1 and 14 and in Tables XII—XV.