A polynomial fitting procedure for the determination of the moments of NMR lines in polymers from the truncated FID

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Abstract
A polynomial fitting procedure (POLFIT) has been developed for the direct calculation of second and higher moments of NMR lines from the FID free induction decay in the time domain. Care must be exercised in taking the proper origin at the middle of the pulse and in choosing the degree of the polynomial given the region of the FID submitted to the fitting procedure. It requires a preliminary optimisation, starting from a theoretical curve with a shape similar to the FID under study. Conditions of stability are found which hold for all dipolar solids, particularly polymers. Extension to the polynomial fitting of a quadrupolar half echo requires a new evaluation of the stability parameters for the strongly oscillating signal.