MICROWAVE SPECTRUM OF $BH_{2}Cl$

Abstract

The microwave spectrum of $BH_{2}Cl$ existing as an intermediate in the reaction between diborane and boron trichloride was observed. The lifetime of this molecule in a brass waveguide cell was found to be less than one second. The rotational constants were determined for $^{11}BH_{2}\,^{35}Cl,\, ^{11}BH_{2}^{37}Cl, ^{10}BH_{2}\,^{35}Cl$, and $^{11}BD_{2}\,^{35}Cl$, and from those the molecular structure ($r_{s}$) was derived as $r(B-H)-1.1916 (2)$ {\AA}, $r(B-Cl) = 1.7353 (5)$ {\AA}, and $\angle HBH=124.22 (3)^{o}$ with planar $C_{2\nu}$ symmetry. The quadrupole coupling constants of Cl, small $x_{zz}$ and large $\eta$ compared to those of related molecules, were obtained and were interpreted in terms of the $\sigma$ ionic character and the $p_{\pi}$ electron backdonation from Cl to B. The dipole moment was determined to be $\mu_{a} = 0.75 (5) D$ for $BH_{2}Cl$.