Optical free-induction decay of paramagnetic molecules in magnetic field

A systematic approach for the calculation of free-induction decay (FID) of paramagnetic species in time domain was developed. The approach allows the prediction of the temporal behavior of FID intensity and polarization in a magnetic field. The technique was illustrated with two examples, a stable paramagnetic molecule (NO) and a very reactive short-lived hydroxyl radical. The results of the calculations are in excellent agreement with available literature experimental data on NO molecule. Significant rotation of the polarization plane, even in a relatively weak magnetic field, potentially will allow selective detection of trace amounts of paramagnetic species (such as short-lived reactive free radicals) on a background signal originating from non-paramagnetic species typically present in great excess.