Molecular Rydberg transitions: field effects in the vacuum ultraviolet

Magnetic-field (Zeeman) and electric-field (Stark) effects provide much information on excited electronic states. Since the field-induced changes are small the technique is applicable only to sharp line-spectra (i.e. to atoms and small molecules). Technological advances have now made possible the measurements of subtle shape changes, a circumstance which opens up field-effect studies of the broad bands which characterize large molecules. The techniques are commonly referred to as 'magnetic circular dichroism' (MCD) and 'electrochromism' respectively. The authors prefer the name 'electric linear dichroism' (ELD) for the latter technique. This paper examines molecular Rydberg states, which usually lie in the VUV region. The authors intent is to categorize these states and to understand the transition from strong core-coupling (valence) to weak core-coupling (Rydberg) to zero core-coupling (continuum). (Auth.)