Distinguished for his work along the following main lines:
1. Spectroscopic studies of the properties of molecules in perturbing environments (e.g., in solution) in an effort to understand the environmental influences on physical and chemical behaviour.
2. Studies of the optical, structural and equilibrium properties of defect solids to provide an understanding of the chemistry of the solid state.
3. The development of high-resolution electron diffraction and a study of fine structural effects to elucidate the mechanism of electron scattering by solids, to apply the method in structure analysis and to obtain information on the behaviour of extremely small crystals.