Infrared difference spectroscopy: Part I. Interpretation of the difference spectrum

Abstract

This paper presents a novel interpretation of difference spectra. The frequencies of the extremes in a difference spectrum do not correspond to the actual band maximum frequencies in the original spectra when the frequency difference of the two bands is less than 150% of the band halfwidth (Hw). In order to alleviate frequency distortions, an application of even derivatives (second and fourth derivatives) of the difference spectrum is proposed. The intensity of the corresponding bands before subtraction can be calculated from the known band frequency and the halfwidth estimated from the difference spectrum. The original calculated intensity may serve as an indicator of the band structure. The calculated band parameters (intensity, frequency, and halfwidth) may further serve as reliable initial values for the band fitting algorithm applied to the original and/or difference spectrum.