Current theories of the effects of static and resonant high frequency magnetic fields on radical pair reaction are presented with a view to establishing how they can form the basis of the high time resolution liquid phase magnetic resonance techniques of MARY and RYDMR. Approximate calculations are performed to reveal RYDMR spectral details for the case of an initial triplet radical pair. The design of unique apparatus to explore the capabilities of the techniques, and routinely collect quantitative data to test theoretical predictions, is described. This includes the development of an ultra-fast waveform scan-digitizing facility which can attain effective sampling rates of up to 20 GHz. The apparatus is employed to provide the first demonstration of recombination exciplex fluorescence from pyrene - dicyanobenzene radical-ion pairs. It is also applied in the dimensional characterization of micellar and microemulsion media prior to their use in enhancing MARY and RYDMR signal intensities from solubilized radical pairs. By means of a laser induced radical fluorescence technique and compartmentalized reaction media, first observations are reported of optically detected RYDMR spectra from neutral radical pairs, the existence of very low field MARY spectral structure and the kinetic effect of a resonant microwave field. The MARY structure is attributed to Heisenberg exchange interaction and shown to be sensitive to microreactor volume.