Knowledge Bank

We have observed the stimulated emission pumping ( SEP ) spectra of highly vibrationally excited methinophosphide ( HCP ) at $16000cm-1-19000cm-1$ above the zero-point energy of linear ground electronic $X~1\Sigma +$ 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 $B=0.663cm-1$ for the highly vibrationally excited $X~1\Sigma +HCP$. In comparison with the $B=0.666cm-1$ 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 $X~1\Sigma +HCP$ have increased from $17.5095\pm 0.0019cm-1$ for $v2=2$ state, observed by infrared $spectroscopy,3$ to $20.0\pm 0.5cm-1$ of the aforementioned $v2=24-30$ states, determined by SEP.