The temperature dependences of the 31P and 1H spin–lattice relaxation times of dichlorophenylphosphine, chlorodiphenylphosphine, and triphenylphosphine have been measured by the adiabatic fast passage method. Both dipolar and spin–rotation interactions contribute to the 31P relaxation mechanism in dichlorophenylphosphine and chlorodiphenylphosphine whereas only dipolar interactions provide the mechanism for the 1H relaxation in all three compounds studied. As the high-temperature limit of the measurements was 160°C, no spin–rotation interactions were observed for the 31P relaxation in triphenylphosphine. The calculations of the approximate potential functions for the internal rotation about the C–P bond in dichlorophenylphosphine and chlorodiphenylphosphine indicate hindered rotation and thus the spin–rotation mechanism arises mainly from spin–over-all-rotation coupling. Spin–rotation constants were estimated for 31P in dichlorophenylphosphine and chlorodiphenylphosphine from relaxation data and shielding constants. In addition to relaxation measurements, the temperature dependences of densities and viscosities of dichlorophenylphosphine and chlorodiphenylphosphine have also been measured.

NMR 19F spin-lattice relaxation times and Raman 435 cm-I doubly degenerate [v,(e)] vibrational-rotation band shapes have been measured in gaseous carbon tetrafluoride at 25·C and densities of 9 to 120 amagat. NMR spin-lattice relaxation times have also been measured over the temperature range of -60 to 4O·C for the above densities. The Fourier transform analysis of the Raman band shapes has allowed us to calculate the reorientational correlation time T6>" Since spin rotation interactions provide the dominant relaxation mechanism for fluorine in CF 4 , then the angular momentum correlation time T J is obtained directly from the 19p T I relaxation times with the assumption that the anisotropy of the spin-rotation interaction tensor is small. A comparison of our experimental T e.' and T J relationship agrees well with that predicted by the dilute gas limit of Gordon's Jand M -diffusion model as extended to classical spherical molecules by McClung.

No abstract

Deuteron longitudinal (Ti) and transversal (T2) relaxation times have been measured for CD3OH adsorbed on the hydroxylic surface of a Xerogel silica gel (the CD3OH-XOH system) and for the related CH3OD-XOD system. These data complement those obtained and discussed earlier for the proton resonance.In the CD3OH-XOH system, is associated with a coverage independent correlation time (jm) = 2.9 X 10-16 exp(5.4 kcal mol-1//??7) sec which has been associated with a molecule tumbling on an adsorption site. T2 seems to be mostly influenced by reorientational effects even though no doublet splitting is apparent in the decay of the magnetization following a 90°p ulse. In the CD3OD-XOD system, has contributions from a molecular diffusion and an exchange term, the latter becoming increasingly important at lower degrees of coverage. At = 1.7, the correlation time associated with and T2 is indeed in the range of those obtained primarily for molecular diffusion: (rod) = 3.15 X 10-14 exp(5.5 kcal mol-1/ RT) sec. For smaller , T2 is influenced by another process and with analogy to what was found for the proton resonance, it appears that this may be a deuteron exchange such as CHsOD2+ + CH3OD. If this is the case, then the quadrupole coupling constant is significantly lower (perhaps 50%) than that used for molecular diffusion. For the two systems studied here, approximately the same distribution of correlation times considered in the proton resonance study is used to account for the experimental data.

No abstract