Abstract: An algorithm for analyzing EPR spectra of solution free radical by use of combining the nonlinear least-squares method with the Monte-Carlo method based on the unconstrained optimization theory is described. This program can fit the experimental EPR spectra data automatically. The EPR spectral parameters, including Lorentzian and Gaussian components to the lineshape, peak height, linewidth,resonance position, and hyperfine couple constant could be extracted from experimental spcctra rapidly with a good accuracy (≤ 5% for the peak height and linewidth, and ≌ 0.002% for the resonance position). The program based on this algorithm has been applied to an EPR data system developed by ourselves which was built on a PC microcomputer system and yield good results.

Key words: EPR, Spectrum analysis, Unconstrained optimization method, Nonlinear least-squares method, Monte-Carlo method