MILLIMETER-WAVE SPECTRUM OF CH3CD3 IN THE 3 LOWEST TORSIONAL STATES

Citation
N. Moazzenahmadi et al., MILLIMETER-WAVE SPECTRUM OF CH3CD3 IN THE 3 LOWEST TORSIONAL STATES, The Journal of chemical physics, 99(4), 1993, pp. 2429-2438
Citations number
33
Categorie Soggetti
Physics, Atomic, Molecular & Chemical
ISSN journal
00219606
Volume
99
Issue
4
Year of publication
1993
Pages
2429 - 2438
Database
ISI
SICI code
0021-9606(1993)99:4<2429:MSOCIT>2.0.ZU;2-W
Abstract
The pure rotational spectra of CH3CD3 in the three lowest torsional st ates has been observed using a mm-wave spectrometer. A total of 87 rot ational frequencies were measured between 230-363 GHz for J=7<--6 to 1 1<--10 in v6=0, 1, and 2, where V6 is the torsional quantum number. Fo r the lowest two torsional states, the spectra have the classic form e xpected for a symmetric top (with no internal rotation) in the ground vibrational state. For V6=2 and for a given (J+1)<--J, a markedly diff erent splitting pattern is observed as a result of the (K,sigma) depen dence of the effective rotational constant B, where sigma labels the t orsional sublevels. In order to identify the individual features in th e (V6=2) spectrum, an assignment procedure was developed which is base d on the fact that the ratio of moment of inertia of the top about the molecular symmetry axis to that of the whole molecule about the same axis is to a very good approximation 1/3. The torsion-rotation Hamilto nian discussed earlier in connection with CH3SiH3 [N. Moazzen-Ahmadi e t al J. Mol. Spectrosc. 119, 299 (1986)] was used to analyze the rotat ional frequencies along with the molecular beam anticrossing data and the origin of the torsional fundamental. Several constants which chara cterize the J-dependence of the energy levels were determined. Effecti ve values for the barrier height V3 and the shape parameter V6 associa ted with the first-order correction in the Fourier expansion of the po tential function were obtained. The effect of redundancies on the inte rpretation of the measurements is discussed.