Kinetic electron spin resonance spectroscopy. Part 5.—Effects of chemically induced dynamic electron polarization

Abstract

A procedure has been developed for measuring the true radical concentration during in situ photolysis e.s.r. experiments, even when the e.s.r. signal is modified as a result of initial electron spin polarization in the photolytically generated radicals. The validity of kinetic e.s.r. studies is thereby extended to shorter times. This procedure depends on an extended kinetic model for chemical induced dynamic electron polarization (CIDEP) incorporating emissive-absorptive (E–A) polarization and initial polarization (IP). The model is tested, using data obtained from a pulse photolysis system, by a study of the behaviour of the semidione radicals of pyruvic acid and biacetyl in alcoholic solvents. For pairs of peaks with the same |∑A_IM_I|, the difference in peak heights represents E–A polarization while the sum incorporates initial polarization, so the two components can be separated. Further experiments have established the viscosity dependences of the two types of polarization.