ALKALI HALIDE DIMERS: MICROWAVE SPECTRUM OF LiFNaF
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Date
1995
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Publisher
Ohio State University
Abstract
The structures of alkali halide dimers have been predicted from numerous calculations ranging from ionic models to ab initi calculations. For symmetrical dimers electron diffraction experiments have confirmed the rhombic structure resulting from these calculations, however, these experimental structures are not sufficiently accurate to critically test the predicted bond lengths and angles. For mixed dimers more precise information may be expected from microwave rotational spectra. In the Berlin laboratory two different techniques have been employed in the rotational study of LiFNaF: a seeded beam with a rotational temperature of about 25 K and cooling by collision in a cold diffusive cell to about 100 K. In the frequency range form 75 to 112 GHz, more than 90 transitions of $^{6}LiFNaF$ and $^{7}LiFNaF$ have been assigned. Due to the high J and K states involved, only a few transitions exhibited partially resolved hyperfine structure from the $^{23}Na$ quadrupolar nucleus. In order to resolve the hyperfine spectum we have used the Fourier-transform microwave (FTMW) spectrometer equiped with NdYAG laser for laser ablation of solid samples at NIST. It is difficult to determine the rotational temperature in the pulsed-beam FTMW spectrometer since only a few rotational states are populated and transitions are widely separated in frequency. The spectra observed in both laboratories were extremely weak in part due to the warmer rotational temperature. In addition to the rotational and hyperfine measurements, we have also examined the Stark effect on $^{7}LiFNaF$ to obtain the dipole moment. The structure resulting from the fit of $I_{a}$ and $I_{b}$ for the two isotopic species is in excellent agreement with a recent ab initio $calculation^{1}$.
Description
1. R.C. Cave and I. OnO, J. Chem. Phys. 99, 9764 (1993).
Author Institution: National Institute of Standards and Technology, Gaithersburg, MD 20899.; Kanagawa Institute of Technology, Kanagawa, Japan; The Graduate University of Advanced Studies, Yokohama 227, Japan.; Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.; Pomona College, 610 N. College Ave., Claremont, CA
Author Institution: National Institute of Standards and Technology, Gaithersburg, MD 20899.; Kanagawa Institute of Technology, Kanagawa, Japan; The Graduate University of Advanced Studies, Yokohama 227, Japan.; Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.; Pomona College, 610 N. College Ave., Claremont, CA