10(4)-FOLD ISOTOPE EFFECT - VIBRATIONAL PREDISSOCIATION IN ARDF

High-resolution sub-Doppler line shapes for ArDF excited into the nu(D F) = 1 manifold are recorded using a tunable laser/slit supersonic exp ansion near-infrared spectrometer. Direct spectroscopic evidence is ob tained for vibrational predissociation (2.6(14) MHz less than or equal to Delta nu(prediss). less than or equal to 4.3(8) MHz), in dramatic contrast with the highly metastable ArHF (nu(HF) = 1) species observed in bolometry studies. To the best of our knowledge, this represents a n unprecedentedly large (> 10(4)-fold), inverse isotope effect. Furthe rmore, a clear dependence of the ArDF predissociation rates on intermo lecular mode, excited in combination with the DF stretch, is observed (61(30) greater than or equal to tau(nu DF) greater than or equal to 3 7(7) ns, tau(nu DF+Sigma bend) greater than or equal to 69(50) ns, tau (nu DF+11bend) greater than or equal to 94(60) ns).