Method of Spectral Subtraction of Gas-Phase Fourier Transform Infrared (FT-IR) Spectra by Minimizing the Spectrum Length

Abstract

A new method of spectral subtraction for gas-phase Fourier transform infrared (FT-IR) spectra was developed for long-path gas measurements. The method is based on minimization of the length of the spectrum that results from subtracting the spectrum of an individual component of a gas mixture (water, CO₂, etc.) from the experimental spectrum of the mixture. For this purpose a subtraction coefficient (k_min) is found for which the length of the resulting spectrum is minimized. A mathematical simulation with two Lorentzian absorption bands was conducted and the limits of application for the proposed method were determined. Two experimental examples demonstrate that a successful result could be achieved in the case when the subtrahend spectrum contains a number of narrow absorption bands (such as the spectrum of water vapor).