Abstract: Time domain ESR is an indispensable technique for the study of paramagnetic relaxation mechanism and the dynamic processes, it is also an important way for enhencement of sensitivity and resolution of spectra. But the frequency domain is still used widely in ESR technique, and the time domain ESR (including FT) is not well developed as fast as FT-NMR now. It is discussed in this paper, and we conclude that time domain ESR would be developed quickly by the application of a slightly different way from PFT-NMR under the improvement of microwave technology, fast pulse circuits and computer techniques.
More recently, saturation recorery and electron spin echo (ESE) are the most attractive methods in time domain ESR. Their basic principles, experimental methods, applications, advantages and limitations are emphatically reviewed in this article. For instance in order to obtain high resolution spectra,the envelope of ESE modulation is transformed to frequency domain by FT (including two dimensional FT), so the weak hyperfine structure of oriented or randomly oriented samples may be analysed. Other example as the ENDOR-ESE has better sensitivity and lower detectable ENDOR frequency over conventional ENDOR.
Furthermore, time-resolved ESR of transient paramagnetic intermediates and transient ESR of molecular triplet state in zero field are also discussed in short. The further development of time domain ESR is expected at last.