Knowledge Bank

Rotational 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 $v2=1$ as well as in the $X2\Pi$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ vibronic states, and the improved molecular constants including the higher order centrifugal distortion constants were obtained. The $v2=1$ vibronic state splits into four vibronic sub-states, $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Delta 5/2,\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Delta 3/2,\mu 2\Sigma$ 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, $NC34S$, in the $X2\Pi 3/2$ state has also been measured and $r0$ structure is derived to be $r0(NC)=1.1805(1)$ {\AA}and $r0(CS)=1.63212(7)\backslash AA$.