A Combined Frequency Analysis of the ν3, ν9, 3ν4 and the Far-Infrared Bands of Ethane: A Reassessment of the Torsional Parameters for the Ground Vibrational State

✍ Scribed by N. Moazzen-Ahmadi

• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 134 KB
• Volume: 214
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.2002.8599

✦ Synopsis

The lowest frequency parallel fundamental band ν 3 of ethane is Raman active. A stimulated Raman spectrum of the Q branch for this band at a resolution of 0.0055 cm -1 has been measured by D. Bermejo et al. (1992, J. Chem. Phys. 97, 7055). The torsion-rotation series in this band with σ = 3, where σ = 0, 1, 2, and 3 labels the torsional sublevels, is perturbed by over 1 cm -1 . The lowest frequency-degenerate fundamental ν 9 is infrared active. A high-resolution (0.0014 cm -1 ) Fourier transform spectrum of this band has been measured by N. Moazzen-Ahmadi et al. (1999, J. Chem. Phys. 111, 9609). The observed torsional splittings for this band are substantially larger than expected from the observed barrier height. Because of a near-degeneracy of the upper level in the ν 9 band with its interacting partner (v 9 = 0, v 4 = 3) a perturbation allowed band 3ν 4 has also been observed. We have carried out a combined analysis of ν 3 , ν 9 , and 3ν 4 together with the far-infrared torsional spectra in the ground vibrational state (gs). A fit to within the experimental error was achieved using 37 parameters. The large torsional splittings in the ν 9 band are attributed to Coriolis-type interactions between the torsional stacks of gs and v 9 = 1 whereas the large shift for the torsion-rotation series with σ = 3 in the ν 3 band is attributed to Fermi-type interactions between the torsional stacks of the gs and v 3 = 1. The introduction of the Fermi-type interactions causes a considerable change in the leading terms in the torsional Hamiltonian for the gs. These changes are quantitatively explained.