Procedure for processing spectroscopic dispersion vs absorption (DISPA) line shapes

Abstract

Abstract For a single Lorentzian line, a plot of dispersion versus absorption (DISPA) gives a perfect circle. For any line shape, the magnitude and direction of displacement of an experimental DISPA plot from its reference circle can be used to diagnose the line-broadening mechanism (e.g. multiple peak positions, multiple peak widths, chemical exchange, saturation broadening, etc.), based on the digitized envelope of a single spectrum. The present algorithm generates normalized absorption and dispersion data sets curves from digitized experimental spectra, and displays normalized reference and experimental DISPA curves in both video and hard copy analog recorder form. In order to symmetrize the final display and reduce compu tation time, the procedure first narrows the frequency range to 20 dispersion peak-to-peak widths on either side of the absorption maximum. The absorption and dispersion baselines are then (separately) flattened. The true absorption peak height and position are accurately estimated usinga polynomial approximation near resonance. The algorithm then normalized the baseline-flattened absorption and dispersion data sets, and plots the corresponding DISPA curve superimposed on a reference circle whose diameter is the calculated absorption peak height. Spacing of the displayed DISPA data points automatically increases with the frequency separation from the center of resonance, for faster plotting and reduced redundancy in display. As a Pascal program, the procedure executes directly on a Bruker Aspect 2000 computer, and can readily be adapted to other computers with Pascal compilers.