Measurements of the proton magnetic resonance at ∼26.9 Mc in titanium hydride samples, ranging in composition from TiH1.61 to TiH1.97, have been made in the temperature range from —196° to about 200°C. The second moment of the proton resonance at the lower temperatures shows that the hydrogen atoms are randomly distributed among the lattice sites which are located tetrahedrally with respect to the titanium atoms. Self-diffusion of the hydrogen atoms narrows the proton resonance above room temperature. The temperature dependence of the correlation frequency for the proton motions, obtained from the linewidths, leads to diffusional activation energies which increase with hydrogen content from 9.4 kcal/g atom for TiH1.607 to 10.2 for TiH1.923. Moreover, the diffusion rate is directly proportional to the number of unfilled tetrahedral holes in the metallic lattice, which indicates that the self-diffusion takes place via a vacancy mechanism. Proton resonance shifts to higher applied magnetic fields were observed. They were measured at room temperature for all specimens and were found to increase from 0.01% for TiH1.607 to about 0.032% for TiH1.969. For these two extreme compositions, the temperature dependence of the shift was measured between —95°C and 190°C and was found to be similar to the bulk susceptibility, the shifts for TiH1.969 exhibiting an anomaly at about 13°C as does the susceptibility. These results are interpreted semiquantitatively in terms of exchange interactions which pair spins of electrons in the conduction band with those of electrons localized on the hydrogen. The results suggest that the hydrogen is held in the lattice by a combination of covalent and ionic bonding, the latter involving a net positive charge on the hydrogen. The general importance of exchange interactions in intermetallic compounds is commented upon.

The conditions under which direct lattice sums of electric potential, field, and field gradient converge are discussed. The analogous conditions under which differences in these lattice sums, for two points in the crystal, converge are also outlined. These conditions are applied to direct lattice sum calculations in crystals in which the ideal lattice is distorted close to a defect of some kind. The conver- gence conditions are then applied to the case of determining the direct lattice sums in crystals in which higher symmetry properties can be invoked, which leads to a knowledge by inspection of the lattice sum at one point in the unit cell.

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The 23Na nuclear magnetic resonance absorption has been observed in the cubic phase of polycrystalline NaCN between about 15° and 170°C, but could not be detected in the orthorhombic phase which forms below 10.5°C. The observed lineshape and its second moment S are compatible with a model in which S= Sd+Sqo+Sq(T), where Sd and SqO are temperature-independent terms, Sd~0.39 G2 resulting from magnetic dipolar interactions of the "rigid lattice" of Na+ ions and SqO~0.16 G2 from first-order nuclear quadrupole interactions with field gradients produced by lattice defects. Sq(T) is a quadrupole broadening term which decreases exponentially from ",13 G2 at 10.5°C to near zero at 170°C.The electric-field gradients (EFG) involved in Sq (T) are attributed to the electric dipoles of the CN-ions, and the temperature dependence, to the averaging out of the gradients by thermally activated reorietations of the CN-ions. The reorientations are deemed responsible for the existence of a cubic phase. They are treated as a random-walk problem yielding algebraic expressions by means of which an activation energy of 6 kcal/mole is obtained from the experimental Sq(T), and 5X1()8 cps at 10°C and 10'0 cps at 150°C are estimated for Vi, the CN-reorientational jump frequency. A discussion is given of the relation between Vj and the nucleation of the cubic to orthorhombic phase transition.2 A wave-packet analysis is used to cast Slater's "new approach" to unimolecular rate theory into quantum form. Qualitative information about the pressure dependence of unimolecular rate constants is obtained, and the activation energy is found to be consistent with Tolman's interpretation.