Koichi Nishikida

Effective path length in attenuated total reflection spectroscopy.

Attenuated total reflection (ATR) spectroscopy is now the most popular sampling technique for the measurement of infrared spectra of condensed phase samples. Most practitioners of ATR spectroscopy use the equation for depth of penetration, d(p), to estimate the path length of the evanescent wave through the sample. However, the effective path length, d(e), of the evanescent wave in an ATR measurement, i.e., the equivalent path length in a transmission measurement that would lead to an absorption band of the same intensity, is a more accurate metric than d(p). In measurements designed to obtain the absorptivity of bands in the spectrum of a strongly absorbing viscous liquid, we have shown that the refractive index used in the expressions for d(e) must be modified to take into account the effect of anomalous dispersion before accurate effective path lengths and band absorptivities can be measured.

CH3I and C2H5I on Au(100): adsorption and reaction

Abstract The adsorption and reaction of CH 3 I and C 2 H 5 I on a Au(100) surface have been studied by a combination of temperature-programmed desorption/reaction (TPD/R), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), reflection-absorption infrared spectroscopy (RAIRS), high-resolution electron energy loss spectroscopy (HREELS) and work function change (Δф) measurements. Both alkyl halides adsorb and desorb mainly in molecular form without decomposition. Only 4% of the first layer CH 3 I molecules dissociate on the surface; the methyl groups formed by this reaction couple to form ethane at ∼ 360 K. By contrast, 20% of the first layer C 2 H 5 I molecules decompose and the final surface reaction products are ethylene, ethane and butane. The dominant product is C 4 H 10 which is formed at ∼ 270 K. Repulsive adsorbate-adsorbate interactions are observed in the first adsorption layer for both alkyl iodides. For CH 3 I (but not for C 2 H 5 I), a high coverage metastable adsorption state characterized by a desorption temperature lower than the multilayer desorption temperature is observed. The structure of the metastable state has yet to be determined, but the results suggest the presence of a CH 3 I bilayer in which the CH 3 I molecules in the first layer are oriented with their CI bonds approximately parallel to the surface and the molecules in the second, metastable layer have a tilted orientation similar to the average orientation in the multilayer. To the best of our knowledge, this is the first observation of a metastable adsorption state for alkyl halides on metal surfaces.

Gel permeation chromatography—Fourier transform infrared study of some synthetic polymers : II. Instrumentation for the characterization of polyethylene

Abstract A high-temperature gel permeation chromatography—Fourier transform infrared (GPC—FT-IR) system was developed to characterize commercially available polyethylene. High-temperature transfer tubing was used to connect the high-temperature flow cell of an FT-IR spectrophotometer and a high-temperature GPC system. The GPC—FT-IR system was calibrated to determine the molecular weight distribution (MWD) and the short-chain branching (SCB) for high-density polyethlene (HDPE) and linear low-density polyethylene (LLLDPE). The MWD and SCB of a commercial LLDPE determined using the present GPC—FT-IR system compared favourably with those measured with a solvent gradient elution fractionation technique where 13 C NMR spectrometry was employed to determine the SCB for the same PE.

Kramers-Kronig Calculation of the Grazing Angle Reflection Spectrum of Barrier Oxide Layer on Aluminum

The nature of the grazing angle reflection spectrum of the thin oxide layer formed on the surface of aluminum was examined by Kramers-Kronig calculations. It was confirmed that the 960-cm−1 peak seen in the grazing angle reflection spectrum corresponds to the absorption band at 738 cm−1 of a low-temperature transition alumina such as γ-Al2O3. The large frequency shift toward higher frequencies is explained in terms of the product between the real and imaginary parts of the refractive index of the oxide. Simulation using the Kramers-Kronig calculation showed, in addition, a very weak structure at about 700 cm−1 in the grazing angle reflection spectrum, which was attributed to a peak shifted from the 590-cm−1 absorption peak of γ-Al2O3.

Development of Attenuated Total Reflection Based Compression Modulation Step-Scan Fourier Transform Infrared Spectroscopy and its Applications to Rheo-Spectral Characterizations of Polymer Films

Dynamic compression modulation attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopic methods have been developed in this paper for characterizing polymer films. To obtain dynamic compression polarized ATR spectra, internal reflection element (IRE) secure assemblies made of tungsten carbide with very high hardness (Knoop hardness of >1000 kgf/mm2) have been designed. These assemblies are mounted on the Harrick Seagull® ATR attachment and measured by step-scan FT-IR spectroscopy. The effect of static compression, air gaps, and refractive index changes were examined. Experimental and simulated results showed that the effect of air gaps between the sample and IRE and refractive index changes of the sample and IRE are negligible at values larger than a static torque of 40 cN m and good signal-to-noise ratios (SNR) and reproducible data can be obtained. Uniaxially and biaxially drawn poly(ethylene terephthalate) films were measured by the presented method. Both bipolar and unipolar bands were observed in the dynamic in-phase ATR spectra, which can be associated with their micro-structural environmental changes. This technique shows promise in evaluating various polymer film materials, including biaxially oriented films, multilayer coated film surfaces, and molecular interactions between polymer–polymer and polymer–additives at the film surface.

Nondestructive quantitative analysis of ethylene-propylene blend polymer by the NIR/ATR/FT-IR method

The attenuated total reflectance Fourier transform infrared (ATR/FT-IR) method in the near-infrared region was found to provide a novel opportunity for nondestructive analysis of ethylene-propylene (EP) blend polymer. The absorption due to the overtone of the C-H stretching vibration at ∼5900 cm−1 was utilized to determine the ratio of two monomer units, the ethylene and propylene units, of the blend polymer, since the overlapping of CH3- and -CH2- is not so prohibitive as in the case of the fundamental C-H stretching vibration at ∼2900 cm−1. The well-known disadvantage of the weak intensity of the overtone absorption, however, was overcome by the choice of the high-sensitivity FT-IR technique.

Investigation of the Christiansen Effect in the Mid-Infrared Region for Airborne Particles

During measurements of open-path Fourier transform infrared spectra, airborne dust may be present in the infrared beam. We have investigated the feasibility of identifying and quantifying the airborne particulate matter from spectra measured in this way. Although the results showed that analysis of the particulate matter was not able to be performed from these spectra, insight into the size and wavelength dependence of the Christiansen effect at wavelengths where the particles absorb strongly was obtained. Airborne particles larger than or equal to the wavelength of the incident radiation give rise to asymmetrical features in the spectrum caused by the Christiansen effect. However, the transmittance at wavelengths where the refractive index of the particles equals that of the atmosphere never reaches 1.0 because of absorption by the particles. As the particle size becomes much smaller than the wavelength of the incident radiation, the Christiansen effect becomes less pronounced and eventually is not exhibited.

Photoacoustic FT-IR Study on Keratin Chemically Bound on the Surface of Silica Gel Particles

The conformation of keratin chemically bound to the surface of silica gel particles has been investigated by means of photoacoustic Fourier transform infrared (PA/FT-IR) spectroscopy. On the basis of the peak positions of the amide I and amide II bands, it is concluded that the keratin thin layer assumes the native α-helix form. It is also noted that the PA/FT-IR method is the only feasible method for observing the IR spectra of the very thin layer of keratin coating on the silica gel particles. The diffuse reflectance technique failed to provide any information on keratin, because of the strong spectral artifact due to the specular reflection at the surface of the silica gel.

Infrared external reflection spectra of Langmuir-Blodgett film on silica substrate

Infrared reflection spectra of bilayer, Langmuir-Blodgett (L-B) films on the glass substrate were measured. Although a reflection spectrum of the substrate is the major feature of the bilayer spectrum, weak spectral features of the L-B film are overlapping. The phase and intensity of each infrared band varies by incident angle and polarization of the infrared radiation. Spectral simulations were carried out to explain the effect of incident angle and polarization on phase and intensity.