Correlated EPR—Optical Spectra of Potassium in Ethylamine—Ammonia Mixtures

Abstract

Extensive electron paramagnetic resonance (EPR) studies of potassium in ethylamine—ammonia mixtures were made over a temperature range of −180° to +100°C and at varying ammonia concentrations up to 68 mole %. Hyperfine splittings, g values, linewidths, and spin concentrations were measured. Optical spectra were measured from −65° to +35°C for a number of the solutions. Correlation of optical and EPR results rules out the assignment of the visible absorption to the monomeric species responsible for hyperfine splitting. The unusual temperature dependence of the EPR spectra cannot be explained in the light of current models, nor can the ammonia dependence be quantitatively interpreted. A model involving equilibrium between atoms and monomers quantitatively describes the temperature dependence. To explain the dependence upon ammonia concentration, it is necessary to consider two monomeric species, one fully solvated by ethylamine and the other involving replacement of ethylamine by one molecule of ammonia. Above about 8 mole % ammonia, computer analysis of the EPR spectra showed the building-in of an extra absorption consisting of a single broad line. The intensity of this absorption relative to the four-line pattern continued to increase until the lines merged at about 25 mole % ammonia. Under varying conditions, the optical spectra showed the three peaks characteristic of metal—amine solutions. Relative intensities were very sensitive to temperature and ammonia concentrations. At low ammonia concentrations only the visible absorption was obtained while the intermediate and infrared absorptions occurred at higher concentrations. The latter two peaks were favored by high temperature, while the visible absorption was more pronounced at lower temperatures. These spectra are discussed in the light of current models for metal—amine solutions.