MILLIMETER-WAVE SPECTRA OF CH3SIH3 IN THE 2 INTERACTING TORSIONAL STATES (V(12)=0, V(6)=3) AND (V(12)=1, V(6)=0)

Pure rotational spectra of gaseous CH3SiH3 in the two interacting tors ional states (v(12) = 0, v(6) = 3) and (v(12) = 1, v(6) = 0) were obse rved in the region from 87 to 197 GHz using a mm-wave spectrometer. He re v(12) and v(6) are, respectively, the principal quantum numbers for the silyl rocking mode and for the torsion. A total of 79 rotational frequencies were measured for J = 4 <-- 3 to J = 9 <-- 8. These new me asurements, 22 rotational frequencies in the (v(12) = 0, v(6) = 3) sta te reported previously, but not analyzed satisfactorily, and 2607 freq uencies from a variety of other earlier experiments were fitted to wit hin the experimental uncertainty by an effective Hamiltonian which inc luded 22 parameters for the ground vibrational state, 12 parameters fo r the (v(12) = 1) vibrational state, and 3 parameters which characteri ze the interactions between these two states. Some of the mm-wave line s are perturbed by about 600 MHz. The form of the effective Hamiltonia n is severely constrained by the large number of precision data on var ious torsional levels in the ground vibrational state, 0 less than or equal to v(6) less than or equal to 3, and on the excited vibrational state (v(12) = 1, v(6) = 0) The model predictions for the (v(12) = 0, V-6 = 4) torsional state and the measurements reported by Wong et al. (J. Mol. Spectrosc. 102, 89, 1983) agree to better than 500 kHz. (C) 1 996 Academic Press, Inc.