A HIGH RESOLUTION ANALYSIS OF THE $\bar{A}A'-\bar{X}^2A'$ TRANSITION OF CASH BY LASER EXCITATION SPECTROSCOPY

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1993

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Ohio State University

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The high resolution spectrum of the $\bar{A}A'-\bar{X}^2A'$ transition of CaSH has been recorded near 650 nm using laser excitation spectroscopy with selected fluorescence detection. While both a-type and b-type rotational transitions have been observed, extensive measurements have been made for the b-type transitions up to $K^{\prime}_{a} = 4$ and $K^{\prime \prime}_{a} = 5.$ Altogether over 3000 rotational lines have been measured and fitted with an A-reduced Hamiltonian. The $\bar{A} ^{2}A$ state has rotational constants $A = 9.693322(46) cm^{-1}, B = 0.1418647(33) cm^{-1}$, and $C = 0.1395810(33) cm^{-1}$ The $\bar{A} ^{2}A'$ state has a band origin at $15380.2847(2) cm^{-1}$, and effective values for the rotational constants $A = 9.090808(78) cm^{-1}, B = 0.1474598(34) cm^{-1}$, and $C = 0.1448042(34) cm^{-1}$. The $\bar{A}^{2}A'$ state is the lower energy Renner-Teller component of the $\bar{A} ^{2}\Pi$ state of the hypothetical linear CaSH molecule, and consequently was found to have a relatively large positive value for the spin-rotation parameter $\varepsilon_{**}$ at $3.44569(26) cm^{-1}$. The upper asymmetry component of the $F_{1}$ spin component of the $K_{a} = 1$ stack and the $F_{2}$ spin component of the $K_{a} = 0$ stack in the $\bar{A} ^{2}A^{\prime}$ state perturb each other with an avoided crossing between $J = 37.5$ and $J = 38.5$. These two spin components interact through the off-diagonal $|\varepsilon_{**} + \varepsilon_{**}|/2$ element of the spin rotation tensor, allowing us to determine its value at $0.065915(46) cm^{-1}.$

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Author Institution: Department of Chemistry, University of Arizona Tucson; Department of Chemistry., University of Waterloo

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