OBSERVATION OF HIGHLY EXCITED VIBRATIONAL LEVELS OF $SiH_{2}$ BY STIMULATED EMISSION PUMPING SPECTROSCOPY
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Date
2001
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Ohio State University
Abstract
$SiH_{2}$ is one of the simplest silicon containing radicals. Similarity and dissimilarity to $CH_{2}$ radical are very interesting from both chemical and spectroscopic points of view. Renner-Teller interaction between the $\tilde{A}^{1}B_{1}$ and the $\tilde{X}^{1}A_{1}$ states and an energy separation between the $\tilde{X}^{1}A_{1}$ and the $\tilde{a}^{3}B_{1}$ states are very important issues in spectroscopy. An analysis of highly excited vibrational levels in the $\tilde{X}$ state should provide some valuable information about them. Thus, we have carried out stimulated emission pumping (SEP) spectroscopy on $SiH_{2}$. In the present study, a pulsed discharge nozzle was used to generate jet-cooled $SiH_{2}$ radical. Precursor of $SiH_{2}$ radical was phenylsilane. The $0_{00}$ rotational levels of the $\tilde{A}(060)$ and (070) levels were used as intermediate levels in the present SEP spectroscopy. Until now, vibrational levels with $v_{2}$ up to $4 (E_{vib} \leq 4000 cm^{-1})$ have been $observed^{a}$. In the present study, 22 vibrational levels in the energy region of $4800 - 8000 cm^{-1}$ were observed. Due to strong $2\nu_{2}:1\nu_{1}$ Fermi and $2\nu_{1}:2\nu_{3}$ Darling-Dennison resonances, vibrational levels having the same polyad quantum number, $P = 2v_{1} + v_{2} + 2v_{3}$, construct polyad structures. The vibrational levels observed belong to polyads of $P = 5 - 8$. Taking these resonance into account, vibrational analysis of the $SiH_{2}$ radical was carried out. In the present analysis, vibrational constants, $x_{13}$ and $x_{23}$, could be determined experimentally, for the first time. Preliminary values are $-74.83 cm^{-1}$ and $-17.58 cm^{-1}$, respectively. Details of the vibrational analysis will be discussed at the presentation.
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$^{a}$H. Ishikawa and O. Kajimoto, J. Mol. Spectrosc. 174, 270 (1995).
Author Institution: Graduate School of Science, Tohoku University; Department of Chemistry, Graduate School of Science, Tohoku University
Author Institution: Graduate School of Science, Tohoku University; Department of Chemistry, Graduate School of Science, Tohoku University