Vibrational predissociation of SF₆ dimers and trimers

IR photo-dissociation spectra of SF₆ clusters have been studied. A He-seeded molecular beam has been attenuated by crossing it with a line tunable cw CO₂ laser of moderate power. - In the electron bombardment beam ionizer (E_el=100eV) small neutral clusters are found to fragment predominantly to the main monomer mass (SF₅⁺). - Predissociation spectra have been calculated for clusters containing up to six SF₆-molecules invoking the dipole-dipole resonance force to lift the degeneracy of the molecule - excited molecule interaction. On the basis of these spectra, dimer and trimer concentrations have been determined quantitatively, for different molecular beam conditions.