Structure of the HX-HX′ dimers

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Abstract
With the advent of accurate measurements on simple molecular systems, the usual electrostatic + polarization + exchange potential has been more and more subject to severe criticism. Owing to the universality of the sole analytical form actually at our disposal and to its reliability in interpreting the spectral response of hydracids trapped in low temperature rare gas matrices, we apply it to the determination of the geometry of molecular dimers HX-HX′, to the subsequent study of the low frequency coupled internal motions (the three coupled anharmonic librational modes describing the orientation of the internuclear axes and the intermolecular vibration mode) and to the calculation of the principal moments of inertia of the rotating complex. Although the calculated mean intermolecular distance appears 5 per cent shorter than the measured one, the close agreement between the internal zero point motion, averaged angular geometries and the beam experiment data clearly shows that such an analytical potential can accurately explain actual structural properties and low temperature dynamical properties of these complexes.