104-fold isotope effect: vibrational predissociation in ArDF

High-resolution sub-Doppler line shapes for ArDF excited into the νDF = 1 manifold are recorded using a tunable laser/slit supersonic expansion near-infrared spectrometer. Direct spectroscopic evidence is obtained for vibrational predissociation (2.6(14) MHz ⩽ Δνprediss. ⩽ 4.3 (8) MHz), in dramatic contrast with the highly metastable ArHF (νHF = 1) species observed in bolometry studies. To the best of our knowledge, this represents an unprecedentedly large (> 104-fold), inverse isotope effect. Furthermore, a clear dependence of the ArDF predissociation rates on intermolecular mode, excited in combination with the DF stretch, is observed (61(30) ⩾ τνDF ⩾ 37(7) ns, τνDF+IIbend ⩾ 94(60) ns).