Dynamic nuclear polarization studies of anomalous CIDNP behavior of benzaldehyde

Abstract

The magnetic field dependence of CIDNP observed during the photolysis of benzaldehyde was measured. At high and low magnetic field limits, respectively, the CIDNP polarization is satisfactorily interpreted in terms of ST o and ST − mixing of radical pair theory. The CINDP polarization observed at around 300 mT, however, cannot be interpreted in terms of radical pair theory. In order to understand this anomalous CIDNP behavior, dynamic nuclear polarization (DNP) was observed. From the observed emissive DNP and the known emissive CIDEP polarization, we conclude that the anomalous CIDNP is due to the transfer of electron spin polarization created by the triplet mechanism to the spin by cross relaxation.