SUBMILLIMETER WAVE SPECTRA OF NCS

$^{a}$NASDA postdoctral fellowAuthor Institution: Institute for Astrophysics and Planetary Sciences, Ibaraki UniversityRotational spectra of NCS in the excited bending vibrational states have not been analyzed in detail, because of difficulty in analysis due to large Renner - Teller effect and anharmonic interactions. We have extended the observation of the pure rotational spectra of NCS in the $v_{2} = 1$ as well as in the $X^{2}\Pi$ ground state up to $J = 53.5$ in the submillimeter wave region. For the ground state, the analysis was straightforward. The measured transition frequencies were fit to a standard effective Hamiltonian for $^{2}\Pi$ vibronic states, and the improved molecular constants including the higher order centrifugal distortion constants were obtained. The $v_{2} = 1$ vibronic state splits into four vibronic sub-states, $^{2} \Delta_{5/2}, {^{2}} \Delta_{3/2}, \mu^{2} \Sigma$ and $\kappa^{2} \Sigma$. As a first attempt, the $\Delta$ and $\Sigma$ states were fitted separately to effective Hamiltonians. The least square fittings converged by including various effective parameters concerned with the P-type doubling. However, the physical significance of these higher order parameters is not clear. It is found that the spin rotation coupling constant, $\gamma$, and the $\Lambda$-type doubling constants, p, q, are significantly different from those for the ground state. We have attempted to analyze the $\Delta$ and $\Sigma$ states simultaneously by taking into account the perturbations from higher vibrational states. An isotopic species, $NC^{34}S$, in the $X^{2}\Pi_{3/2}$ state has also been measured and $r_{0}$ structure is derived to be $r_{0}(NC) = 1.1805(1)$ {\AA}and $r_{0}(CS)= 1.63212(7) {\AA}$