Field cycling by fast NMR probe transfer: Design and application in field-dependent CIDNP experiments

A novel field-cycling unit with fast digital positioning of a high-resoluti on nuclear magnetic resonance probe in a spatially varying magnetic field i s described and used to measure CIDNP spectra of the amino acid-dye (histid ine-bipyridyl) photoreaction system in the range between 0 and 7 T. The pat tern of nuclear polarization varies with the magnetic field. In particular, strong polarization with an emission/absorption pattern (multiplet effect) is found at low field for two histidine ring-protons with scalar coupling below 3 Hz visible only because of the high resolution made possible by the new field-cycling setup. Also for the CH2 protons in the beta-position a m ultiplet effect is observed having a pattern changing with magnetic field. By analysis of the spin nutation the non-Boltzmann population differences o f the nuclear levels have been determined.