OBSERVATION OF HIGHLY VIBRATIONALLY EXCITED $\tilde{X} ^{1}\Sigma^{+}$ HCP BY STIMULATED EMISSION PUMPING SPECTROSCOPY
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Date
1994
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Ohio State University
Abstract
We have observed stimulated emission pumping (SEP) spectra of vibrationally excited $\widetilde{X} ^{1}\Sigma^{+}$ HCP via its $\widetilde{C} ^{1}A^{\prime}$ state. We measured high resolution SEP spectra of two thirds of the $22 500 cm^{-1} -23 200 cm^{-1}$ region. Since the $\widetilde{C} - \widetilde{X}$ transition is a parallel one, only $l^{\prime} = 0$ levels are accessible by allowed transitions. When the P(J) line is used an a pump transition, the R(J-2) and P(J) lines appear in the spectrum. We used P(2), P(4),\ldots . P(10) lines as pump transitions. There, 20 vibrational levels were found. Among them, 17 levels have definitely J = 0 level. This indicates that they are definitely $l^{\prime} = 0$ levels. In the previous SEP study via the $\widetilde{A} ^{1}A^{\prime\prime}$ $stale^{1}$, only pure bend overtone levels were observed in this region. It is expected that there is one Franck-Condon bright series (0, 38,0),(0, 36.1),(0, 34,2)\ldots (0,24, 7). Considering the level density, combination levels involving H atom radial motion must be excited. The B constants of these levels are in the range $0.63 cm^{-1} - 0.76 cm^{-1}$. Compared with the B constant in the vibrational ground state, $0.666 cm^{-1}$, a B constant of more than $0.7 cm^{-1}$ is so large as to be of diagnostic significance. The 4 levels which have B constant of more than $0.72 cm^{-1}$ can be assigned as members of similar (n, v, 0),(ns v-2, 1)\ldots series built on $n \neq 0$ quanta of H---(CP) stretch. Detailed analysis will be presented.
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1. Y.-T.Chen, D.M. Watt, R.W. Field and K.K. Lehmann, J. chem. Phys. 93, 2149 (1990) .
Author Institution: Department of Chemistry, Massachusetts Institute of Technology
Author Institution: Department of Chemistry, Massachusetts Institute of Technology