Millimeter-Wave Molecular-Beam Spectroscopy: Alkali Chlorides

The pure rotational spectra of the alkali chlorides were investigated in the 0.96- to 3-mm range of the microwave region with the molecular-beam spectrometer earlier developed at Duke University. Introduction of Teflon microwave lenses and high-pass microwave filters improved this spectrometer so that measurements into the submillimeter region were possible, to an accuracy of better than one part in ${10}^6$. Dunham's solution for the diatomic molecule was applied in interpretation of data. Improved values for $B_e$, ${\alpha }_e$, and ${\gamma }_e$ were obtained for most molecules studied. The centrifugal distortion constants $D_e$ and ${\beta }_e$ were obtained from the rotational spectra for the first time for all molecules measured. From the latter two constants, accurate values of ${\omega }_e$ and ${\omega }_e{x}_e$ were derived. Other derived quantities are: potential coefficients, isotopic mass ratios, moments of inertia, and internuclear distances. For most of these quantities, the accuracies obtained surpass those from previous measurements.