Millimeter-Wave Spectra of $CH_{3}SiH_{3}$ in the Two Interacting Torsional States $(v_{12} = 0, v_{6} = 3)$ and $(v_{12} = 1, v_{6} = 0)$

Abstract

The pure rotational spectra of gaseous $CH_{3}SiH_{3}$ in the two interacting torsional states $(v_{12} = 0, v_{6} = 3)$ and $(v_{12} = 1, v_{6} = 0)$, where $v_{12} = 1$ is the lowest lying excited vibrational state (silyl rock), were observed in the region from 87 to 196 GHz using a mm-wave spectrometer. A total of 81 rotational frequencies were measured for $J = 7 \leftarrow 6$ to $J = 9\leftarrow 8$ in the $(v_{12} = 0, v_{6} = 3)$ and $(v_{12} = 1, v_{6} = 0)$ states. These new measurements, 24 frequencies in $(v_{12} = 0, v_{6} = 3)$ state reported earlier $Wong et al.^{1}$, but not fitted satisfactorily, and frequencies from previously reported experiments were fitted to within the experimental uncertainty by an effective Hamiltonian which included 22 parameters for the ground vibrational state, 11 parameters for the $v_{12} = 1$ vibrational state, and 3 parameters which characterize the interactions between these two states. Some of the mm-wave lines are perturbed by about 600 MHz. The global data set contained 2712 frequencies. The form of the effective Hamiltonian is constrained by the large number of precision data on various torsional levels in the ground vibrational state, $0\leq v_{6} \leq 3$, and the excited vibrational state $(v_{12} = 1, v_{6} = 0)$. The model predictions for the $(v_{12} = 0, v_{6} = 4)$ torsional level and the measurements reported by $Wong et al.^{1}$ agree to within 400 KHz.