Vibrational predissociation, tunneling, and rotational saturation in the HF and DF dimers

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Abstract
The high-resolution spectra of the intramolecular stretching bands of the HF and DF dimers have been recorded with a tunable difference-frequency laser. These measurements yield considerable information about the dynamics of hydrogen bonding in these complexes. Vibrational predissociation is observed as a non-pressure-dependent excess linewidth for the ‘‘bound-H’’stretching band of the HF dimer, but no excess linewidth is observed for the ‘‘free-H’’ stretching band of the HF dimer or for either band of the DF dimer. An unusually large vibrational dependence to the interconversion tunneling frequency is observed for both species, with about a factor of three reduction from the ground state splitting upon excitation of any of the intramolecular stretches. The K subband origins obtained from the A/B hybrid free-H stretching band of the HF dimer exhibit an irregular pattern indicating anomalous centrifugal distortion effects suggestive of rotational saturation of the angular orientation of the hydrogen bond.