Journal of Chemical Physics, Vol.104, No.16, 6225-6243, 1996
Probing Hydrogen-Bond Potentials via Combination Band Spectroscopy - A Near-Infrared Study of the Geared Bend Van-der-Waals Stretch Intermolecular Modes in (HF)(2)
High resolution near infrared spectra of the two lowest frequency intermolecular modes in HF-stretch excited states of (HF), have been characterized using a slit-jet infrared spectrometer. In the spectral region surveyed, ten vibration-rotation-tunneling (VRT) bands are observed and assigned to the low frequency "van der Waals stretch" (nu(4)) and "geared bend" (nu(5)) intermolecular modes, in combination with either the hydrogen bond acceptor (nu(1)) or donor (nu(2)) high-frequency intramolecular HF stretches. Analysis of the rotationally resolved spectra provide intermolecular frequencies, rotational constants, tunneling splittings, and predissociation rates for the nu(4)/nu(5) intermolecular excited states. The intermolecular vibrational frequencies in the combination states display a systematic dependence on intramolecular redshift that allows far-IR intermolecular frequencies to be reliably extrapolated from the near-IR data. Approximately tenfold increases in the hydrogen bond interconversion tunneling splittings with either nu(4) or nu(5) excitation indicate that both intermolecular modes correlate strongly to the tunneling coordinate. The high resolution VRT line shapes reveal mode; specific predissociation broadening sensitive predominantly to intramolecular excitation, with weaker but significant additional effects due to low frequency intermolecular excitation. Analysis of the high resolution spectroscopic data for these nu(4) and nu(5) combination bands suggests strong state mixing between what has previously been considered van der Waals stretch and geared bend degrees of freedom.
Keywords:QUASI-ADIABATIC CHANNELS;HF DIMER;VIBRATIONAL PREDISSOCIATION;HIGH-RESOLUTION;FLUORIDE DIMER;ENERGY SURFACE;INTRAMOLECULAR DYNAMICS;SPECTRA;ROTATION;COMPLEXES