Electron spin resonance spectroscopy study of solvated alkali-metal atoms at X- and Q-band frequencies

Abstract

Electron spin resonance studies of frozen solutions of alkali metals in hexamethylphosphoramide (HMPA) show a variety of distinct, localised electronic states. These range from atom-like solvated centres with up to ca. 70% electron spin density on the alkali-metal cation to weakly localised ion-pair states. The e.s.r. spectra of solvated-atom species in sodium, potassium and rubidium solutions over a wide range of temperatures (4–250 K) and at both X- and Q-band frequencies (ca. 9 and 32 GHz, respectively) are reported. The high-field (Q-band) e.s.r. spectra for potassium and rubidium solutions show clear evidence of anisotropic coupling. The effect of this anisotropy on both A and g of the more usual X-band (low-field) spectra can be simulated using a complete Breit–Rabi reconstruction of line positions. A secondary, ‘submultiplet’ splitting of the characteristic sodium hyperfine quartet is found to be virtually temperature independent whilst being dependent on both m_I and the magnetic field. The possibility of an interaction of two inequivalent sodium monomers is discussed. The origin of this secondary submultiplet splitting is described in terms of multiple trapping sites for the solvated sodium atom.