The rotation-vibration spectra of allene and allene-d₄

Abstract

The infrared absorption spectra of allene and allene-d₄ vapor have been measured over the spectral range 250-5000 cm⁻¹ with a prism spectrometer. The infrared data, together with previously obtained Raman spectra, enable a complete vibrational analysis that satisfies the product rule well for all vibrational species. The torsional vibration is located at 865 cm⁻¹ in allene and 615 cm⁻¹ in allene-d₄. Fine structure was resolved for all perpendicular fundamental bands except that of the lowest frequency in both compounds. With help of the Ζ-sum rule, a modified equation of H. H. Nielsen and the statistical weights of the rotational levels, the fine structure is analyzed to yield a complete set of Ζ-values for both molecules and a moderately accurate value for the moment of inertia about the figure axis. The latter gives for the HCH angle the figure 113^°; ± 1^°; if one assumes a C∃ H distance of 1.071A.