INTRAMOLECULAR THERMAL MOTION IN LIQUID PROPIONIC-ACID (-RELAXATION STUDY .1.(DMSO), A PROTON MAGNETIC)

The proton magnetic relaxation times T-1 and T-2 of the three propioni c acid species, HOOCC2D5, DOOCCH2-CD3, and DOOCCD2CH3, have been measu red at a resonance frequency v = 12 MHz as a function of the temperatu re in the range 80 < T/K less than or equal to 270. 33 mol % DMSO-d(6) had to be added to the propionic acid in order to make measurements f easible in the supercooled region. T-1 measurements were performed at the frequencies v = 30 MHz and v = 48 MHz as well. Isotopic dilution e xperiments with constant content of propionic acid and varying degree of deuteration were made to obtain the intramolecular relaxation rates . The proton NMR spectra of the three propionic acid species were reco rded at T = 130 K. From all these data, correlation times for the vari ous proton-proton vectors were derived. It turned out that to each mot ion a slow and a fast mode contribution exists, however, the results a re not compatible with the model of a molecule as a system of rigid bo dies connected by axes about which rotation occurs. The various motion al modes are described by continuous Cole-Davidson correlation time di stributions. For all group time correlation functions g(t) of the seco nd degree spherical harmonics after transcription in the Kohlrausch-Wi lliams-Watts formalism are presented.