DEUTERIUM-ISOTOPE EFFECTS ON THE ULTRAFAST SOLVENT RELAXATION OF FORMAMIDE AND N,N-DIMETHYLFORMAMIDE

We present the results of our study on the ultrafast solvent dynamics of the amides formamide (FA), N,N-dimethylformamide (DMF), and their d euterated analogs HCOND2 (d(2)-FA) and DCON(CD3)(2) (d(7)-DMF) using f emtosecond optical-heterodyne-detected Raman-induced Kerr effect spect roscopy (OHD-RIKES). Using nearly transform-limited 50 fs optical puls es and the Fourier-transform relationship, we have studied the liquid dynamics in the frequency range from 0.6 to 400 cm(-1). In comparison to the depolarized Rayleigh spectroscopy technique, OHD-RIKES is shown to provide more accurate and detailed information about the low-frequ ency region that includes the rotational reorientation, librational, a nd collision-induced dynamics. The effect of deuterium isotope substit ution on the inertial as well as diffusive reorientational dynamics of these amide liquids is discussed.