Knowledge Bank

K = 0 transitions have been assigned in the microwave rotational spectra for six isotopic variations of the $B2H6-HCl$ dimer. The homonuclear dimens, with $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}B-\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}B$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}B-\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}B$, have tunneling splittings of several MHz, while the mixed species with $\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}B-\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}B$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}B-\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}B$ show no tunneling. This contrasts with $B3H6-HF$ which has a torsionally averaged, linear B-B-F structure with no evidence of $tunneling.1$ The line center of the $\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}B\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}B-H\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}ClJ=3\to 4,K=0$ transition is at 10 186.777 MHz. The splitting due to tunneling is 2.587 MHz, a value which decreases somewhat for both lower and higher J. In the $\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}B\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}B-H\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}Cl$ species the splitting for $J=3-4$ decreases to 2.325 MHz while that in $\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}B\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}B-H\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}Cl$ is 4.726 MHz. This indicates that the tunneling motions involve both subunits. Work is in progress to locate the $K=\pm 1$ transitions so that accurate rotational constants and the structure can be deduced. The results so far indicate a near linear H-B-Cl configuration.