JET SPECTROSCOPY OF THE $\nu_{4}$ BAND OF HYDROGEN FLUORIDE TETRAMER IN THE $714 cm^{-1}$ REGION
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Date
1999
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Ohio State University
Abstract
Using our slit-jet, infrared diode laser spectrometer, we have observed a rotationally resolved parallel band centered at $714 cm^{-1}$ in a pulsed molecular beam formed by expanding a mixture of 4\% HF in helium through a $200 \mu m \times 12$ cm slit with a backing pressure of ca. 1000 Torr. A set of excited and ground state spectroscopic constants were fit simultaneously to a data set of 204 transitions using a symmetric top, semi-rigid rotor Hamiltonian. The fit constants are $\nu_{0}714.7849(1) cm^{-1}, B^{\prime}=0.129614(5) cm^{-1}, (C^{\prime} -B^{\prime})- (C^{\prime \prime} -B^{\prime \prime})=0.001339(6) cm^{-1}, D^{\prime}_{j}=4.9(2)\times 10^{-7} cm^{-1}, D^{\prime}_{JK}= -1.1(2)\times 10^{-6}cm^{-1}, D^{\prime}_{K}-D^{\prime \prime}_{K}=-2.81(8)\times 10^{-6} cm^{-1}, H^{\prime}_{JKK}= -2.0(2)\times 10^{-8}cm^{-1}, H^{\prime}_{KKK}- H^{\prime \prime}_{KKK}-4.68(6)\times 10^{-8} cm^{-1}, B^{\prime \prime}=0.132059(5)cm^{-1}, D^{\prime \prime}_{J}=5.1(2) \times 10^{-7} cm^{-1}, D^{\prime \prime}_{JK}=-1.3(2)\times10^{-6} cm^{-1}, H^{\prime \prime}_{JKK}=-6(2)\times 10^{-9} cm^{-1}$, and the RMS deviation of the obs - cales is $0.00045 cm^{-1}$. We have also observed two other bands in the 700 to $775 cm^{-1}$ region: one band is a strongly perturbed perpendicular band centered at $752 cm^{-1}$ with $B^{\prime\prime} = 0.133 cm^{-1}$ and the other band is a perturbed parallel band centered at $741 cm^{-1}$ with $B^{\prime \prime} = 0.0755 cm^{-1}$. For hydrogen fluoride tetramer and pentamer, theory predicts (Maerker, $et al.)^{a}$ planar, oblate symmetric top structures at their global minima with $B_{c}$ values of 0.136 and $0.0767 cm^{-1}$ for $(HF)_{4} (C_{4h}$ symmetry) and for $(HF)_{5} (C_{5h}$ symmetry), respectively. We have tentatively assigned the $714 cm^{-1}$ band as the $\nu_{4} (A_{u})$ HF out-of-plane torsion of the tetramer, the $752 cm^{-1}$ band as the $\nu_{13} (E_{u})$ HF in-plane torsion of the tetramer, and the $741 cm^{-1}$ band as the $\nu_{4} (A^{\prime \prime})$ HF out-of-plane torsion of the pentamer.
Description
$^{a}$ C. Maeker, P.R. Schlyer, K.R. Liedl, T.-K. Ha, M. quack, M.A. Suhm, J. Comp. Chem. 18 1695 (1997).
Author Institution: Pacific Northwest National Laboratory, P. O. Box 999, Mail Stop K8-88
Author Institution: Pacific Northwest National Laboratory, P. O. Box 999, Mail Stop K8-88