Numerical calculations of the powder pattern of the central component shifted by the second-order nuclear quadrupole interaction in solids have been performed for various values of the asymmetry parameter, η. Shape functions have been obtained in units of (νQ2/6νL) (a—¾) for η=0.1, 0.2, ···, 1.0, at 0.1 intervals. Also, positions of special points such as infinities and steps of the shape function have been determined as functions of η. Effects of the dipolar broadening of the single-crystal resonance upon powder patterns have been estimated for the case of η=0.5. Influences of anisotropic magnetic shift were also discussed on powder patterns obtained experimentally. These relations are useful for simple and rapid determinations of η and νQ from the second-order powder pattern.
Proton magnetic resonance techniques have been used to study the molecular motions occurring in some dimethyl silicones. The substances investigated were cured Silastic 80, 400 Gum, and 200 Fluid (viscosity grade 20 centistokes at 25°C). Measurements were made of the absorption line shape from 77°K to room temperature, and of the spin-lattice relaxation time, T1, from 160°K to 415°K. Evidence is found for the existence of methyl group reorientation about the triad axis, segmental motions about the Si–O bonds and a form of intramolecular ``spiral'' motion of the (CH3)2Si groups. The relation of the latter motion to the difference in macroscopic properties of natural and silicone rubbers is discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.