General introduction

Abstract

Most magneto optical effects have their root in the Zeeman splitting of energy levels. The symmetry properties of the magnetic interaction are contrasted with those of an electric interaction. In molecular spectroscopy, measurement of the Zeeman splittings yields the magnetic moments of molecules in both ground and excited states. When lines are broad, the new technique of magnetic circular dichroism is particularly useful for assigning spectra and determining magnetic moments. The Cotton-Mouton effect in absorption bands is briefly considered.