(a) Nuclear Spin Interactions in Molecules. It has become clear that high-

resolution nuclear-resonance experiments can give a great deal of information relative to the geometrical and electronic structures of molecules. It is believed that all observed spectral structures can be accounted for on the basis of the Hamiltonian- _ = h H ~yi ( I- i) + J.. I. I. i i j>i where H is the applied magnetic field, yi is the gyromagnetic ratio of nucleus i, Ii is its spin operator, and 6 and Jij are coupling constants characteristic of the elec-tronic wavefunctions of the molecule. We are attempting to justify the form of this Hamiltonian in intermediate coupling cases, and to correlate the coupling constants with simple descriptions of the molecular wavefunctions. Standard radiofrequency techniques are being used, with particular attention to the magnetic field uniformity and stability which will permit resolution of lines separated by approximately 1 part in 108 of the total field. (b) Molecular Motion in Solids. Large-scale motion in solids can have important effects on the macroscopic properties of substances in which they occur. This fact is particularly evident in solid-state diffusion and chain twisting in polymers such as rubber. Nuclear-resonance linewidth measurements can give rather direct infor-mation on the types of motion that are present and on their activation energies. We are applying this method to cases that are not practicably accessible by other methods, with special reference to ion and terminal group reorientation. Results which have been obtained deal with Co(NH+++ and MF ions and-CH 3 and-CF 3 groups in various crystal lattices