MICROWAVE SPECTRUM OF $NaBH_{4}$
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Date
1991
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Publisher
Ohio State University
Abstract
The rotational spectrum of $NaBH_{4}$ was observed in the millimeter-wave region using a high temperature absorption bell. The observed spectrum of $NaBH_{4}$ showed the pattern of a symmetric top molecule: strong and weak for $K=3n$ and $3n+1$, respectively, because of the nuclear spin statistical weight for $C_{3}v$ symmetry. The rotational and centrifugal distortion constants for the $^{11}B$ and $^{10}B$ species were determined. The observed rotational constants of $Na^{11}BH_{4}$ and $Na^{10}BH_{4}$, combined with the assumption that $r(B-H_{b}) - r(B-H_{L}) = 0.04$ {\AA} and $\theta(H_{b}-B=H_{t}) = 111^{\circ}$ gave estimates for r(Na-B) and r(B-H) to be 2.308 $\pm 0.006$ {\AA} and 1.28 $\pm$ 0.10 {\AA}, respectively. This bond length obtained for Na-B is much shorter than the reported value in crystal; 3.08 {\AA}. The bond lengths derived indicate that $NaBH_{4}$ has a tridentate molecular structure with three bridging hydrogens. This result agrees with those of ab initio calculations. In addition, two other sets of the rotational spectra were observed; one had a larger centrifugal distortion constant $D_{JK}$ than that of the ground state, while the other a negative centrifugal distortion constant $D_{JK}$, and the K structures of both the spectra were irregular at $K=0$, 1, and 2. These spectra are assigned to the excited vibrational states of $NaBH_{4}$.
Description
Author Institution: Kanagawa Institute of Technology; Institute for Molecular Science