STIMULATED EMISSION SPECTROSCOPY OF SINGLET $CH2$: THE BENDING BARRIER HEIGHT AND THE $\bar{a}-\bar{b}$ SPLITTING

$^{1}$ P.R.Bunker and T.J.Seara J. Chem. Phys. 83 4866 (1985) $^{2}$ G.Duxbury and Ch.Jungen Molec. Phys. 63 981 (1988)Author Institution: Department of Chemistry, University of PennsylvaniaStimulated Emission Pumping (SEP) has been used to detect the bending vibrational overtones of $\bar{a}^{1}A_{1} CH_{2} (\nu_{2} = 2, 3$, and 4). The vibrational term values and rotational constants, were determined. Comparison between the bending potential model calculations$^{1,2}$ and experimental results places the barrier height of the bending motion for $\bar{a}^{1}A_{1} CH_{3}$ at about $9800 cm^{-1}$ and the $\bar{a}$ and $\bar{b}$ state splitting at $8300 cm^{-1}$. As a result, the numbering of the $\bar{b}^{1}B_{1}$ bending vibrational levels needs to be changed from $\nu_{2}$ to $_{2}^{-2}$. Furthermore, abnormally strong $\Delta K_{2}=3$ transitions in the $\bar{a} \leftarrow $b band and the tunneling effect in the high bending overtones will be discussed