A Theory of the Electronic Structures and Spectra of Negative Ions

Abstract

Abstract Some aromatic anions in solutions show absorption spectra with many sharp bands in the visible and ultraviolet regions. It is pointed out that this is rather remarkable in view of the fact that aromatic molecules have very small electron affinities, nearly zero or even negative, in the gas phase. It is then emphasized that the potential for the electron in the negative ions is much more localized than the Coulomb potential. Accordingly, some of the features of the negative ions are deduced by the use of a simple well-type potential. The important conclusions obtained are: 1) Negative ions may have discrete electronic energy levels not only in the E≤0 region but also in the E>0 region, that is, higher than the detachment energy. 2) The larger the domain of the potential well for the electron, the discrete energy levels can exist at the higher energy. 3) These energy levels at E>0 should, of course, be unstable, mostly leading rapidly to the electron detachment, but their lifetime are the longer, the larger the domain of the potential well. These consequences seem to account well for the above-mentioned spectra of aromatic anions. Other features of the negative ions and the nature of the charge-transfer states in the charge-transfer complexes are also discussed.