The molecular beam spectrum of the hydrogen fluoride dimer has been investigated in detail. Microwave and radiofrequency transitions of (HF)2, HFDF, and (DF)2are reported for both theKa=0 andKa=1 rotational levels. The results provide information on the structure of the dimers and on the nature of the intermolecular potential energy surface. The average Fndash;F distance is shown to be approximately 2.78 Aring; but with a probably significantly shorter equilibrium distance. The nonhydrogen bonded hydrogen atom is bent 63deg;plusmn;6deg; from the Fndash;F axis. In addition, analysis of the perpendicular electric dipole moment indicates a nonlinear hydrogen bond. The large centrifugal distortion effects and the unusual quantum mechanical tunneling provide a crude model for the potential surface associated with the hydrogen bond; the effective bond stretching force constant is (1.36plusmn;0.03)times;104dynthinsp;cmminus;1.
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