Introduction to Chemically Induced Magnetic Polarization

Abstract

Both esr and nmr lines with anomalous intensities have been observed in chemically reacting systems. The effects have been called chemically induced dynamic electron and nuclear polarization (CIDEP and CIDNP respectively). They arise from species (radicals or reaction products) that are formed with non-equilibrium spin state populations. CIDEP has first been found by Fessenden and Schuler in 1963 (1), but did not receive much attention at the time. Several years later in 1967 the CIDNP effect was discovered independently by Bargon and Fischer (2) and by Ward and Lawler (3). It took, however, until 1969 before a beginning was made in the understanding of both phenomena. The Radical Pair Mechanism (4, 5) in one form or another, later complemented by the Triplet mechanism (6), seems to be capable of explaining virtually all CIMP effects and some related phenomena such as the magnetic field dependence of product yields (7) and of triplet yields in electron-transfer reactions (8) and the magnetic isotope effect (9).