ISOTOPIC-SUBSTITUTION OF A HYDROGEN-BOND - A NEAR-INFRARED STUDY OF INTRAMOLECULAR VIBRATIONS IN (DF)(2)

High resolution near infrared spectra of the two high frequency intram olecular modes in (DF)(2) have been characterized using a slit-jet inf rared spectrometer. In total, four pairs of vibration-rotation-tunneli ng (VRT) bands are observed, corresponding to K=0 and K=1 excitation o f both the nu(2) (''bound'') and nu(1) (''free'') intramolecular DF st retching modes. Analysis of the rotationally resolved spectra provides vibrational origins, rotational constants, tunneling splittings and u pper state predissociation lifetimes for all four states. The rotation al constants indicate that the deuterated hydrogen bond contracts and bends upon intramolecular excitation, analogous to what has been obser ved for (HF)(2). The isotope and K dependence of tunneling splittings for (HF)(2) and (DF)(2) in both intramolecular modes is interpreted in terms of a semiclassical 1-D tunneling model. High resolution line sh ape measurements reveal vibrational predissociation broadening in (DF) (2): 56(2) and 3(2) MHz for the nu(2) (bound) and nu(1) (free) intramo lecular stretching modes, respectively. This 20-fold mode specific enh ancement parallels the greater than or equal to 30-fold enhancement ob served between analogous intramolecular modes of (HF)(2), further eluc idating the role of nonstatistical predissociation dynamics in such hy drogen bonded clusters. (C) 1996 American Institute of Physics.