Dynamics of spin-polarized photoelectrons in rubidium-tetrahydrofuran solutions

We present a Fourier transform EPR study of photoexcited rubidium-tetrahydrofuran solutions (Rb/THF), in the absence and presence of the complexing chelate 222 cryptand (Kp), Rb/THF/Kp. The temporal behavior of the EPR signals is interpreted in terms of two components participating in the complex processes, i.e., the spin-polarized photoelectrons and the solvated electrons that are coupled to the alkali-metal cations and, when present, to the cryptand molecules. The spin polarization mechanism is due to the radical pair mechanism, which is induced by charge transfer to solvent as a result of the photoabsorption. Spin relaxation times, measured directly in these systems, are discussed in terms of a site-exchange narrowing mechanism and a spin-rotation coupling mechanism in Rb/THF solutions and by collision-induced electron transfer in Rb/THF/Kp solutions.