Angular Dependence of Diffuse Reflectance Infrared Spectra. Part II: Effect of Polarization

1987 ◽  
Vol 41 (5) ◽  
pp. 791-797 ◽  
Author(s):  
Paul J. Brimmer ◽  
Peter R. Griffiths
Keyword(s):  
Angular Dependence ◽  
Infrared Spectra ◽  
Diffuse Reflectance ◽  
Absolute Intensity ◽  
Absorption Bands ◽  
Reflectance Measurement ◽  
Wire Grid ◽  
Optical Geometry ◽  
Ft Ir ◽  
Diffuse Reflectance Infrared

The magnitude of specular and diffuse Fresnel reflectance from powdered samples was investigated with the use of an FT-IR spectrogoniophotometer with wire-grid polarizers mounted in front of and behind the sample. Specular Fresnel reflectance maintains the polarization of the incoming infrared beam and can therefore be eliminated by crossing the orientation of the second polarizer relative to the first. For neat samples, diffuse Fresnel reflectance was found to be only slightly affected by the presence of the two polarizers. While specular Fresnel reflectance is affected by the optical geometry used in making the reflectance measurement, diffuse Fresnel reflectance is unaffected by optical geometry and can only be eliminated by dilution of the neat sample. For dilute samples, the optical geometry and the orientation of the two polarizers slightly affect the absolute intensity of absorption bands, but do not change relative band intensities or band positions.

Angular Dependence of Diffuse Reflectance Infrared Spectra. Part I: FT-IR Spectrogoniophotometer

1986 ◽  
Vol 40 (2) ◽  
pp. 258-265 ◽  
Author(s):  
Paul J. Brimmer ◽  
Peter R. Griffiths ◽  
N. J. Harrick
Keyword(s):  
Angular Dependence ◽  
Infrared Spectra ◽  
Diffuse Reflectance ◽  
Reflectance Spectra ◽  
Absorption Bands ◽  
Diffuse Reflectance Spectra ◽  
Preliminary Results ◽  
Optical Geometry ◽  
Ft Ir ◽  
Diffuse Reflectance Infrared

An optical arrangement is described which allows diffuse reflectance infrared spectra to be collected by the use of a variety of incident angles and collection geometries. In the first phase of this study, the reflectance from a nonabsorbing powder and the intensity of the reststrahlen band in quartz were monitored as a function of optical geometry. The contribution of Fresnel reflectance was found to be very dependent on optical geometry, and the effect on the intensity of absorption bands in diffuse reflectance spectra is demonstrated. Based on these preliminary results, some suggestions for minimizing Fresnel reflectance through the optimization of diffuse reflectance optics are made.

Angular Dependence of Diffuse Reflectance Infrared Spectra. Part III: Linearity of Kubelka-Munk Plots

1988 ◽  
Vol 42 (2) ◽  
pp. 242-247 ◽  
Author(s):  
Paul J. Brimmer ◽  
Peter R. Griffiths
Keyword(s):  
Angular Dependence ◽  
Infrared Spectra ◽  
Diffuse Reflectance ◽  
Strong Absorption ◽  
Absorption Bands ◽  
Linear Region ◽  
Line Configuration ◽  
Munk Function ◽  
Before And After ◽  
Diffuse Reflectance Infrared

The linearity of plots of the Kubelka-Munk function against concentration is investigated for weak and strong absorption bands in the spectrum of a typical organic analyte, caffeine. The linear region is extended when measurements are made with an off-axis optical geometry, in comparison to an in-line configuration. For the latter configuration, the linearity is improved when crossed polarizers are placed before and after the sample.

Diffuse Reflectance FT-IR Characterization of Active Sites under Reaction Conditions: The Production of Oxygenates in the CO/H2 Reaction

1994 ◽  
Vol 48 (10) ◽  
pp. 1208-1212 ◽  
Author(s):  
J. J. Benítez ◽  
I. Carrizosa ◽  
J. A. Odriozola
Keyword(s):  
Infrared Spectra ◽  
Active Sites ◽  
Diffuse Reflectance ◽  
Reaction Conditions ◽  
In Situ Drifts ◽  
Ft Ir

The reactivity of a Lu2O3-promoted Rh/Al2O3 catalyst in the CO/H2 reaction is reported. Methane, heavier hydrocarbons, methanol, and ethanol are obtained. In situ DRIFTS has been employed to record the infrared spectra under the actual reaction conditions. The structure of the observed COads DRIFTS bands has been resolved into its components. The production of oxygenates (methanol and ethanol) has been correlated with the results of the deconvolution calculation. Specific sites for the production of methanol and ethanol in the CO/H2 reaction over a Rh,Lu2O3/Al2O3 catalyst are proposed.

Applications of Diffuse Reflectance FT-IR to Pigment Photodecomposition in Paint

1982 ◽  
Vol 36 (2) ◽  
pp. 155-157 ◽  
Author(s):  
D. B. Chase ◽  
R. L. Amey ◽  
W. G. Holtje
Keyword(s):  
Ir Spectroscopy ◽  
Infrared Spectra ◽  
Diffuse Reflectance ◽  
Spectral Subtraction ◽  
Ft Ir ◽  
Ft Ir Spectroscopy

Diffuse reflectance FT-IR spectroscopy is used to obtain infrared spectra of paints directly on paper panels. The binder contribution to the spectrum can be effectively eliminated by spectral subtraction and the spectra of photodecomposition products are obtained. Comparison with reference spectra allows the determination of the photodecomposition mechanism.

scholarly journals Analysis of functional groups in atmospheric aerosols by infrared spectroscopy: sparse methods for statistical selection of relevant absorption bands

2016 ◽  
Vol 9 (7) ◽  
pp. 3429-3454 ◽  
Author(s):  
Satoshi Takahama ◽  
Giulia Ruggeri ◽  
Ann M. Dillner
Keyword(s):  
Infrared Spectra ◽  
Atmospheric Aerosols ◽  
Quantitative Prediction ◽  
Calibration Model ◽  
Vibrational Modes ◽  
Aerosol Composition ◽  
Absorption Bands ◽  
Calibration Models ◽  
Ft Ir ◽  
Selection Of

Abstract. Various vibrational modes present in molecular mixtures of laboratory and atmospheric aerosols give rise to complex Fourier transform infrared (FT-IR) absorption spectra. Such spectra can be chemically informative, but they often require sophisticated algorithms for quantitative characterization of aerosol composition. Naïve statistical calibration models developed for quantification employ the full suite of wavenumbers available from a set of spectra, leading to loss of mechanistic interpretation between chemical composition and the resulting changes in absorption patterns that underpin their predictive capability. Using sparse representations of the same set of spectra, alternative calibration models can be built in which only a select group of absorption bands are used to make quantitative prediction of various aerosol properties. Such models are desirable as they allow us to relate predicted properties to their underlying molecular structure. In this work, we present an evaluation of four algorithms for achieving sparsity in FT-IR spectroscopy calibration models. Sparse calibration models exclude unnecessary wavenumbers from infrared spectra during the model building process, permitting identification and evaluation of the most relevant vibrational modes of molecules in complex aerosol mixtures required to make quantitative predictions of various measures of aerosol composition. We study two types of models: one which predicts alcohol COH, carboxylic COH, alkane CH, and carbonyl CO functional group (FG) abundances in ambient samples based on laboratory calibration standards and another which predicts thermal optical reflectance (TOR) organic carbon (OC) and elemental carbon (EC) mass in new ambient samples by direct calibration of infrared spectra to a set of ambient samples reserved for calibration. We describe the development and selection of each calibration model and evaluate the effect of sparsity on prediction performance. Finally, we ascribe interpretation to absorption bands used in quantitative prediction of FGs and TOR OC and EC concentrations.

Anomalous Dispersion Effects in Diffuse Reflectance Infrared Fourier Transform Spectroscopy: A Study of Optical Geometries

1989 ◽  
Vol 43 (2) ◽  
pp. 267-274 ◽  
Author(s):  
D. M. Hembree ◽  
H. R. Smyrl
Keyword(s):  
Fourier Transform ◽  
Diffuse Reflectance ◽  
Specular Reflection ◽  
Fourier Transform Spectroscopy ◽  
Anomalous Dispersion ◽  
Fresnel Reflection ◽  
Absorption Bands ◽  
Dispersion Effects ◽  
Diffuse Reflectance Infrared ◽  
Reflectance Measurements

In this report, the two most common diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) optical geometries (on-axis and off-axis) are investigated in terms of adherence to the Kubelka-Munk theory. It was found that specular reflection, whether in the form of regular Fresnel reflection or diffuse Fresnel reflection, is the major cause of spectral distortion in typical diffuse reflectance measurements. A discussion of the origin of the variation in specular background associated with resonances is presented. Once the adverse effects of specular reflection are minimized, the linear relationship between response and concentration predicted by Kubelka-Munk theory was found to extend to concentrated samples. Up to a point, this was the case even for intense absorption bands where anomalous dispersion leads to large changes in specular intensity.

Diffuse Reflectance Infrared Spectroscopic Characterization of Silica Dehydroxylation

1990 ◽  
Vol 44 (1) ◽  
pp. 69-75 ◽  
Author(s):  
Robert L. White ◽  
Aurobindo Nair
Keyword(s):  
Force Constant ◽  
Diffuse Reflectance ◽  
Spectroscopic Characterization ◽  
Absorption Bands ◽  
Stretching Vibration ◽  
Diffuse Reflectance Infrared ◽  
Highly Strained ◽  
Infrared Absorption Bands ◽  
Absorbance Band

Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) is employed to study the dehydroxylation of amorphous silica. Dehydroxylation results in the appearance of infrared absorption bands at 1022, 1107, and 1240 cm−1 assigned to asymmetric stretching vibrations for three different siloxane bridge types. The 1107-cm−1 absorbance band represents a siloxane bridge that is indistinguishable from bulk species. The 1022-cm−1 absorbance band represents a siloxane bridge with a bond angle that is smaller than the bulk, with little change in the stretching vibration force constant. The 1240-cm−1 absorbance band derives from a siloxane bridge characterized by a stretching force constant significantly larger than that of bulk siloxane bridges. This band may be indicative of a highly strained or broken siloxane bridge.

New Method for Pollen Identification by FT-IR Spectroscopy

2003 ◽  
Vol 57 (1) ◽  
pp. 23-27 ◽  
Author(s):  
C. S. Pappas ◽  
P. A. Tarantilis ◽  
P. C. Harizanis ◽  
M. G. Polissiou
Keyword(s):  
Fourier Transform ◽  
Ir Spectroscopy ◽  
Diffuse Reflectance ◽  
Pollen Grains ◽  
Comparison Method ◽  
Plant Origin ◽  
The Family ◽  
Ft Ir ◽  
Diffuse Reflectance Infrared ◽  
Ft Ir Spectroscopy

A new methodology for identification of pollen was developed based on FT-IR spectroscopy. Pollen samples of twenty different plant species were collected and the diffuse reflectance infrared Fourier transform (DRIFTS) and KBr pellet spectra were recorded. Libraries of spectra were created. Spectra of unknown plant origin pollen were recorded and compared with those of the corresponding pollen library and the match value was measured automatically using the appropriate software (OMINC ver. 3.1). From the same pollen samples, microscopic slides were prepared and the photographs of the pollen grains were used as a second comparison method. Using light microscopy, the pollen identification is usually limited to the family or generic name, while FT-IR spectroscopy can distinguish species belonging to the same genus. This method is simple and fast, and when the DRIFTS technique is used the sample is not destroyed.

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