Apodization effects in Fourier transform infrared difference spectra

Abstract

Dans le cas de bandes intenses des artefacts dus au processus d'apodisation peuvent apparaître dans les spectres infrarouges obtenus par transformée de Fourier. Ces effets ont déjà été étudiés sur des spectres obtenus par différence pour des fonctions d'apodisation de type boxcar ou triangulaire. Ce travail présente des simulations numériques réalisées avec une fonction d'apodisation de type Happ-Genzel couramment employée dans les instruments modernes. Pour comparer les performances des fonctions d'appareil de type boxcar, triangulaire, ou Happ-Genzel nous avons calculé (i) les artefacts apparaissant dans les spectres obtenus par différence ; (ii) la variation de l'absorbance apparente au sommet d'un pic d'absorption en fonction de l'absorbance vraie ; (iii) une mesure intégrée de l'erreur due à ces artefacts pour une bande d'absorption à profil lorentzien. L'étude est faite pour des valeurs de p (rapport de la largeur totale du pic à mi-hauteur à la résolution) qu'on rencontre couramment en spectroscopie de transmission d'échantillons solides ou translucides.Abstract. -Artifacts may occur in Fourier transform infrared (FTIR) spectra due to the apodization of the interferograms of intense bands. Selected examples of boxcar and triangular apodization effects on difference spectra have been previously reported. This paper reports the first such calculation performed for the Happ-Genzel apodization function, which is often used on modern spectrometers. In order to compare boxcar, triangular, and Happ-Genzel apodization functions we calculate (i) difference-spectrum artifacts, (ii) apparent versus true peak absorbances, and (iii) a measure of integrated artifact area for several true peak intensities of Lorentzian-band shapes. Values of p (ratio of full bandwidth at half height to nominal resolution) are emphasized which commonly occur in the transmission-mode spectroscopy of transparent or translucent solid samples.

Reconstitution properties of micellar casein powder: Effects of composition and storage

“…The spectra were obtained at a resolution of 4 cm À1 by co-adding 32 interferograms. A Happ-Genzel apodization function (Bretzlaff & Bahder, 1986) was applied prior to Fourier transformation. Each sample was measured in triplicate.…”

Using Fourier transform IR spectroscopy to analyze biological materials

“…The interferometer mirror velocity may also have an effect on SNR 3 . Weighting the interferogram with an apodization function will also contribute to a reduction in SNR, as this smoothing effect can incorporate spectral artifacts while one is attempting to optimize the information contained 93 . In general, the square root of the number of co-additions is proportional to the SNR, and therefore an increased number will enhance the SNR 94 .…”

Atmospheric pressure glow discharge in air used for ethanol conversion: experiment and modelling

“…Triangular apodization function was chosen, which leads to the diffraction contours of the lines [18]. For spectroscopic analysis, the exhaust gases from the plasma-chemical reactor have passed through 5.7 -centimeter cuvette, which was previously heated up to 90 o C in order to prevent condensation of water and alcohol vapors.…”