Knowledge Bank

Using the two techniques of photoelectron spectroscopy and external perturbation in absorption spectroscopy, it is now rather easy to identify Rydberg transitions and to calculate their term values, which may alternatively be regarded as excited state ionization potentials. Such data is now available for a wide range of compounds and displays the following trends. In oxides, amines, olefins, ketones, parafins, etc., the 3d term value is 12 000-14 000 $cm-1$, regardless of molecular composition; the 3p term value is near-constant at 17 000-22 000 $cm-1$, but that of 3s can be strongly dependent upon the nonchromophoric structure of the molecule. The 3s term values of oxides vary from 40 000 to 24 000 $cm-1$ depending upon the bulkiness of the groups attached to the chromophore. In amines, the 3s term is much less dependent upon the nonchromophoric groups, and is virtually independent of it in parafins and olefins. The oscillator strengths in Rydberg transitions of different 1-value also vary strongly but in a systematic manner when the bulkiness of the nonchromophoric groups increases.