LARGE PARITY SPLITTING AS AN INDICATION OF THE HCP $\longleftrightarrow$ CPH "ISOMERIZATION"
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Date
2006
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Ohio State University
Abstract
We have been investigating the HCP $\longleftrightarrow$ CPH ``isomerization'' of HCP molecule by the stimulated emission pumping (SEP) spectroscopy. In the previous study, we recorded SEP spectra in the energy region up to 26800 cm$^{-1}$ in the $\tilde{X}$ state from the vibrational ground level. This value is very close to the height of the ``isomerization'' barrier (27400 cm$^{-1}$) predicted by the theoretical study. It was found that several vibrational levels exhibit complicated perturbation patterns due to the Coriolis type interaction}. Strong Coriolis perturbations in the energy region near the ``isomerization'' barrier are predicted by Jacobson and Child based on their spherical pendulum model} \underline{\textbf{114}}, 262 (2001).}. They also pointed out that the parity splitting in $\ell \ne 0$ levels should be a good spectroscopic indication of the ``isomerization'' in addition to the rotational constants. \par Until now, due to the rotational selection rules, only the $\ell=0$ levels were observed in the energy region above 20000 cm$^{-1}$. However, using a perturbed level in the $\tilde{C}$ state as an intermediate, we have succeeded in recording SEP spectra which have sampled $\ell=1$ levels in the 26250 -- 27300 cm$^{-1}$ region in the $\tilde{X}$ state, in the present study. As a result, we have found a good relation between the rotational constants and the parity splittings. Larger-$B$ levels exhibit larger parity splittings. For instance, A vibrational level having a $B_{\rm ave.}$ of 0.76 cm$^{-1}$ exhibits $\Delta B = 0.13 {\rm cm}^{-1}$, while another level having a $B_{\rm ave.}$ of 0.62 cm$^{-1}$ exhibits $\Delta B = 0.03 {\rm cm}^{-1}$. The $\Delta B$ of the former level is about 4 times larger than that of the latter. It is confirmed that the parity splitting is one of the spectroscopic indications of the ``isomerization'' of the HCP/CPH system as expected. \par
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Author Institution: Department of Molecular Science and Material Engineering, Graduate School of Science and Technology, Kobe University, Kobe 657-8501, Japan; Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan