Knowledge Bank

The rotation-inversion spectrum of the ground state of the HF dimer has been studied in a one meter stainless steel cell under equilibrium conditions at dry ice temperature in the frequency region of 60 to 125 GHz. Both K = 0 and K = 1 subband transitions have been observed, thus extending the previous $observations1,2$ to higher J. In addition, with the aid of infrared combination differences, 13 P, Q, and R lines of the K = 2 subband have been identified. A fit of the higher J K = 0 and K = 1 subband lines Observed in this work as well as those previously $measured(1,2)$ yields improved values for the centrifugal distortion constants. The observed microwave K = 2 lines were combined with Infrared combination differences to obtain the spectroscopic constants of the K=2 state. The inversion spitting and B rotational constants for this state are: [FIGURE] where the + or$-$sign indicates respectively the lower or upper tunnelling component and $E2+-E0+$ is the energy difference between the hypothetical J = 0 level of the K = $2+$ state and the ground state. Not unexpectly the centrifugal disortion constants for the K = 2 levels are found to be anamolously large. Because of the nonridigity of the molecule it is necessary to treat each subband independently. $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$T. R. Dyke, B. J. Howard and W. Klemperer, J. Chem. Phys. 56. 2664 (1972). $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$B. J. Howard, T. R. Dyke, and W. Klemperer, private communications.