Pure absorption electron spin echo envelope modulation spectra by using the filter-diagonalization method for harmonic inversion

Harmonic inversion of electron spin echo envelope (ESEEM) time-domain signa ls by filter diagonalization is investigated as an alternative to Fourier t ransformation. It is demonstrated that this method features enhanced resolu tion compared to Fourier-transform magnitude spectra, since it can eliminat e dispersive contributions to the line shape, even if no linear phase corre ction is possible. Furthermore, instrumental artifacts can be easily remove d from the spectra if they are narrow either in time or frequency domain. T his applies to echo crossings that are only incompletely eliminated by phas e cycling and to spurious spectrometer frequencies, respectively. The metho d is computationally efficient and numerically stable and does not require extensive parameter adjustments or advance knowledge of the number of spect ral lines. Experiments on gamma-irradiated methyl- alpha-D-glucopyranoside show that more information can be obtained from typical ESEEM time-domain s ignals by filter-diagonalization than by Fourier transformation. (C) 1999 A cademic Press.