Pulsed electron double resonance (PELDOR) and its applications in free-radicals research

Abstract

The papers related to the theoretical background and experimental investigations by pulsed electron double resonance (PELDOR) are reviewed. The main aim of this pulsed ESR application is to study the dipole-dipole spin interaction. In PELDOR the ESR spectrum is excited by two ESE pulses at frequencyω a and additional pumping pulse atω b. Decay functionV(T) of the ESE signal, when the time intervalT between the first ESE pulse and pumping pulse is varied, contains the information on dipole-dipole couplings in the spin system. The kinetics ofV(T) decay strongly depends upon distance, mutual orientation inside interacting spin pairs and space distribution of radicals throughout the sample. The distances between spins which were measured or estimated using PELDOR in the papers reviewed are in the range of 15 ÷ 130 Å. This pulsed ESR technique turns now to be a powerful supplement to conventional ESE in studying the free radicals space distribution..