Torsional Splitting in the ν5 Fundamental Infrared Band of CH3CD3 and 13CH3CD3

✍ Scribed by F. Lattanzi; C. di Lauro; C. Claveau; A. Valentin; G.D. Nivellini

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 110 KB
• Volume: 207
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.2001.8343

✦ Synopsis

The ν 5 fundamental (C-C stretching) of CH 3 CD 3 shows a resolved torsional structure, caused by perturbations due mainly to the linear dependence of the torsional potential barrier on the normal coordinate Q 5 . We were able to analyze this structure and to assign vibration-rotation transition wavenumbers for all five torsional components, classified according to the symmetry species of the G (3) 18 extended molecular group. The torsional splitting pattern is qualitatively similar to that of a nondegenerate vibrational state with an even number of excited torsional quanta v 6 . Explorative calculations show that the main perturber system should consist of the torsional components of the vibrational ground state correlating with v 6 = 4 in the high barrier limit. The strength of the perturbation on the E r 0 torsional components of ν 5 increases rapidly with r , the E 40 component being the most affected. The observed transition wavenumbers can be reasonably fitted by a simplified model containing independent effective vibration-rotation parameters for the five different torsional components of ν 5 , for both CH 3 CD 3 and 13 CH 3 CD 3 . The trend of the determined values of the effective vibrational wavenumbers and rotational parameters over the torsional components supports the proposed vibration-torsion interaction mechanism, responsible for the observed torsional splittings. A strong anomaly observed in the rotational intensity distribution of ν 5 is discussed.