Knowledge Bank

The microwave spectra of the HCCS and DCCS radicals ($X2\Pi 1$) in both $CCS(\nu 5)$ and $H(D)CC(\nu 4)$ bending vibrational states were observed in the freuency range of 160 400 GH2 with a de discharge of the $C2H2$ (or $C2D2$) and $CS2$ gas mixture. The rotational transition series for the vibronic $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Delta 2,3yz(\nu 5),\mu \kappa 2\Sigma (\nu 5),2\Pi 3/2(2\nu 5),2\Delta 5/2(\nu 4)$ and $\mu 2\Sigma (\nu 4)$ states were assigned. The analysis of the effective molecular constants showed that the values of the $\tau eff$ constants of the vibronic $\mu \kappa 2\Sigma$ states were different from each other by 2 3 GHz, which could not be explained by the up-to-date Renner-Teller theory for a single bending mode. This abnormal Renner-Teller effect may be understood by a new vibronic interaction theory, which was developed by us to consider the cross vibronic interaction between the two bending modes.