AbstractA new, convenient method of analyzing the spin polarization of a non-equilibrium system of N coupled nuclei is described and applied to photo-reactions exhibiting chemically induced dynamic nuclear polarization (CIDNP). It is based on the Fourier analysis of the variation of NMR line intensities as a function of the radio frequency excitation pulse length. A relationship between the spectral components at various harmonic order and the alignment in the spin multiplet is established. In application to the Norrish type I photolysis of cyclodecanone we demonstrate that at low magnetic field the rate determining step in the reaction kinetics depends on the mutual orientation of at least four pairs of non-equivalent spins.
Norrish’ type I and II reactions and their role in the building of photochemical science