15min:

I. OZIER, Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada V6T 1Z1; and Laboratorium für Physikalische Chemie, Eidgenössische Technische Hochschule, CH-8093 Zürich, Switzerland; A. BAUDER, Laboratorium für Physikalische Chemie, Eidgenössische Technische Hochschule, CH-8093 Zürich, Switzerland; W. L. MEERTS, Department of Molecular and Laser Physics, NSRIM, University of Nijmegen, NL-6500 GL Nijmegen, The Netherlands; N. MOAZZEN-AHMADI, Department of Physics and Astronomy, University of Calgary, Calgary, AB, Canada T2N 1N4; J. SCHRODERUS, Department of Physical Sciences, University of Oulu, FIN-90014, Linnanmaa, Finland.

The vibration-torsion-rotation Hamiltonian in CH₃SiH₃ has been investigated using Fourier transform microwave methods and tunable sideband far-infrared spectroscopy. Four different studies have been carried out. First, the Q-branch of the torsion-vibration difference band (v₁₂=0, v₆=3) (v₁₂=1, v₆=0) has been measured between 17.8 and 26.6 GHz. When three quanta of the torsional mode ₆ are excited in the ground vibrational state (gs) for ( =-1) torsional sublevels with K=6, these transitions become allowed through resonant Coriolis-like coupling to the lowest lying degenerate mode ₁₂ with no quanta of ₆ excited. Second, direct l-doubling transitions in the state (v₁₂=1, v₆=0) have been observed between 8.3 and 17.5 GHz for both =0 and =\pm 1. In the limit that the intervibrational interactions vanish, the -splitting between lines of the same J would be difficult to resolve, but frequency differences of more than 1 GHz due to these interactions have been determined. Third, the (J=1 0) spectrum just below 22 GHz has been re-measured with higher resolution for 0\leq v₆\leq 4 in the gs and for (v₆=0) in ₁₂. Finally, the (J=45 44) spectrum near 1 THz has been obtained for 0\leq v₆\leq 2 in the gs. A global data set of 3423 frequencies has been formed by merging the present 123 measurements with the data set used recently in the simultaneous analysis of the ₁₂ and ₅ bands. By refining the (gs/ ₁₂/ ₅) Hamiltonian developed in this earlier work, a good fit to within experimental error has been obtained by varying 45 parameters. The grouping of the torsional motion with rotational rather than vibrational degrees of freedom will be discussed.