Observation of Highly Vibrationally Excited $\tilde{X} ^{1}\Sigma^{+} HCP$ by Stimulated Emission Pumping Spectroscopy

1. K. K. Lchmann, S. C. Ross and L L Lohr, J. Chem. Phys.,82, 4460 (1985). 2. J. W. C. Johns, H. F. Shurvell and J. K. Tyler, Can. J. Phys., 47, 893 (1969). 3. J.-M. Garneau and A. Cabana. J. Mol. Spectrosc., 87, 490 (1981).Author Institution: Department of Chemistry, Massachusetts Institute of Technology, Cambridge; Department of Chemistry, Princeton UniversityWe have observed the stimulated emission pumping ( SEP ) spectra of highly vibrationally excited methinophosphide ( HCP ) at $16000 cm^{-1} -19 000cm^{-1}$ above the zero-point energy of linear ground electronic $\tilde{X} ^{1}\Sigma^{+}$ state. At such high energy, HCP is predicted to undergo a large-amplitude-bending vibration, where the H atom is approximately half-way $(\angle HCP -90^{\circ})$ from HCP to another chemical network, $``HCP''.^{1}$ The observed SEP signals of large-amplitude-bending states (0.26,0). (0,28,0) and (0,30,0). and of a bending C---P stretching combination state (0,24, 1), have enabled us to deternine the rotational constants $B = 0.663 cm^{-1}$ for the highly vibrationally excited $\tilde{X} ^{1}\Sigma^{+} HCP$. In comparison with the $B = 0.666 cm^{-1}$ values of those states with only a few vibrational $quanta,^{2}$ the rotational energy pattern of HCP remains almost unchanged even when large-amplitude-bending motions are excited. On the other hand, the energy separations between vibrational angular momenta $\ell =0$ and $\ell =2$ of the same vibrational level of $\tilde{X} ^{1}\Sigma^{+}HCP$ have increased from $17.5095 \pm 0.0019 cm^{-1}$ for $v_{2} =2$ state, observed by infrared $spectroscopy,^{3}$ to $20.0 \pm 0.5cm^{-1}$ of the aforementioned $v_{2} =24-30$ states, determined by SEP