The effect of alkali-metal ion association on the electronic spectra of the mononegative ions of naphthalene and anthracene

Abstract

The energies of the absorption bands of mononegative ions of naphthalene and anthracene in tetrahydrofuran solution in the presence of alkali-metal cations show slight shifts when Li⁺ or K⁺ is substituted for Na⁺. This is interpreted as an ion-association effect, and it appears that for all three metal ions the M⁺R^- ion-pairs are practically undissociated in solutions of concentration ∼ 10^-3 M at 300°k. A simple perturbation theory is given and is found to fit the observed trends of individual bands reasonably well. The absence of hyperfine structure from interaction with the K nucleus in the electron spin resonance spectra of tetrahydrofuran solutions of potassium naphthalenide found in the recent work of Atherton and Weissman is attributed to the rather small isotropic hyperfine interaction constant for ³⁹K.