Infrared diode laser spectroscopy

Three types of lasers (double-heterostructure 66 K InAsSb/InAsSbP laser diode, room temperature, multi quantum wells with distributed feedback (MQW with DFB) (GaInAsSb/AlGaAsSb based) diode laser and vertical cavity surface emitting lasers (VCSELs) (GaSb based) have been characterized using Fourier transform emission spectroscopy and compared. The photoacoustic technique was employed to determine the detection limit of formaldehyde (less than 1 ppmV) for the strongest absorption line of the v₃ + v₅ band in the emission region of the GaInAsSb/AlGaAsSb diode laser. The detection limit (less than 10 ppbV) of formaldehyde was achieved in the 2820 cm⁻¹ spectral range in case of InAsSb/InAsSbP laser (fundamental bands of v₁, v₅). Laser sensitive detection (laser absorption together with high resolution Fourier transform infrared technique including direct laser linewidth measurement, infrared photoacoustic detection of neutral molecules (methane, form-aldehyde) is discussed.     

Recent applications of FT-IR/PAS studies in catalysis

Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) is one of the main IR techniques which successfully can be applied in catalysis research. There will be presented recent examples of this spectroscopic technique application.     

纳米材料ZrO2的傅里叶变换红外光声光谱研究

首次报道单斜ＺｒＯ２纳米材料在各种微晶粒度下的傅里叶变换红外光声光谱（ＦＴ－ＩＲ－ＰＡＳ），发现随着粒度的减小，波数低于１０４８ｃｍ＾－＾１的谱线强度减弱，而波数高于１０４８ＣＭ＾－＾１的谱线强度增加，一些谱线位置有红移，并观察了压力效应。对上述量效应进行 初步解释。     

抗蒸汽干扰的液体傅里叶变换红外光声探测器

本文描述一种以微音器作声耦合器件的、适用于与傅里叶交换红外光谱仪联用的液体光声光谱探测器.实验结果表明;这种光声探测器能够消除水蒸汽吸收对样品吸收的干扰,是一种测水量溶液样品傅里叶变换红外光声谱的方法.     

FT-IR/PAS of the EDTA adsorbed on alumina with the various surface areas

Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) was applied to investigate samples with the adsorbed species formed during preparation metal supported catalysts. In the studies conducted gamma alumina with the various surface areas was used. Samples prepared by the double impregnation method (DIM) have similar spectral characteristic. This allowed to conclude that surface areas of γ-Al₂O₃ used had no influence on the nature of the examined species.     

Broadly tunable quantum cascade laser in cantilever-enhanced photoacoustic infrared spectroscopy of solids

An external cavity quantum cascade laser (EC-QCL) is applied in the photoacoustic detection of solid samples. The EC-QCL used has a broad tuning range of 676 cm^?1 (970–1,646 cm^?1) in the mid-infrared region, which enables accurate broadband spectroscopy of large molecules. The high spectral power density of the EC-QCL is combined with an extremely sensitive optical cantilever microphone of the photoacoustic detector to achieve an ultimate sensitivity. The carbon black, polyethylene, and hair fiber samples were measured with the EC-QCL photoacoustic detection using electrical amplitude modulation to demonstrate the possibilities of the setup. The same measurements were repeated with a Fourier transform infrared (FTIR) spectrometer combined with a photoacoustic detector for a comparison. The EC-QCL photoacoustic setup yielded roughly a decade better signal-to-noise ratios than the FTIR setup with the same measurement time.     

Synthesis and Vibrational Spectroscopic Investigation of Methyl L-Prolinate Hydrochloride: A Computational Insight

In our present work, methyl L-prolinate hydrochloride has been synthesized from L-proline amino acid and characterized by Fourier transform infrared and Fourier transform Raman spectra via experimental and computational methods. Ab initio Hartree-Fock and density functional theory (B3LYP) calculations have been made for the structure, and atomic charge distributions were also predicted for the title compound by using the 6-311++G(d,p) basis set. Predicted vibrational frequencies have been assigned and compared with experimental Fourier transform infrared and Fourier transform Raman spectra. The thermodynamic properties such as heat capacity, enthalpy, entropy, and Gibbs energy have been calculated at different temperatures. The calculated highest occupied molecular orbital and lowest unoccupied molecular orbital energy show the charge transfer behavior within the molecule.     

Infrared photoacoustic spectroscopy in catalysis and surface science

The analysis of solid samples can often be a difficult problem for the researchers dealing with infrared (IR) spectroscopy. In conventional absorption spectroscopy the measurement of absorption is transferred to that of the radiation transmitted through the sample. Three methods stand out as being more suitable for studying solid materials. These methods are: diffuse reflectance (DR), photoacoustic spectroscopy (PAS), and Fourier transform (FT) Raman. All three methods require little or no sample preparation, and therefore are ideal for the samples that may change during the preparation as mineral oil mulls or KBr disks. In the case of PAS, the adsorbed radiation is determined directly via its heat and hence the sound produced in the sample. Fourier transform infrared PAS (FT-IR/PAS) is one of the main IR techniques which can be successfully applied in catalysis and surface science research. Recent examples of this spectroscopic technique application will be presented.     

Mid-infrared photoacoustic spectroscopy of solids using an external-cavity quantum-cascade laser

We describe the use of a pulsed external-cavity quantum-cascade laser (EC-QCL) for the acquisition of mid-IR photoacoustic (PA) spectra of solids. The EC-QCL employed in this work operates from 990 to 1075 cm(-1) (9.30-10.10 microm). A gas-microphone PA cell was used as the detector, and the signal was demodulated using a lock-in amplifier. PA EC-QCL spectra of solids display bands significantly narrower than those in corresponding PA Fourier transform infrared spectra.     

Spectroscopic studies of alumina-supported nickel catalysts precursors: Part I. Catalysts prepared from acidic solutions

Nickel alumina-supported catalysts were prepared from acidic solutions of nickel nitrate by the CIM and DIM methods (classical and double impregnation, respectively). The catalysts exhibited different nickel species due to the existence of various metal-support interaction strengths. As a consequence, the reducibility and other surface properties changed as a function of the preparation method. The aim of this work was to study the interaction between the metal precursor and the alumina surface by means of FT-IR (Fourier transform infrared) and FT-IR/PAS (FT-IR photoacoustic spectroscopy).     

基于傅里叶变换中红外光声光谱的污渍鉴定

采用中红外光声光谱,对一起交通事故中当事人身上的污渍和当事货车上的尘土样本进行定性鉴定。结果表明,当事人左手肘部的污渍与身体其他部位的污渍明显不同,但与当事货车右车身上的污尘具有高度的相似性,表明当事人的左肘与当事货车的右车身发生了直接的碰擦,这为交通事故的定责提供了直接依据;因此,红外光声光谱可为中微量物质的精细鉴定提供了新手段,在物证分析中具有潜在的应用前景。     

共焦扫描光声层析成像技术的研究

报道了一种新的光声层析成像技术－光声傅里叶变换共焦扫描成像技术，并用该技术获得了强散射物质（生物组织）的层析图像，纵向分辨能力小于0．1mm，横向分辨率小于4mm。     

Silicon rich silicon oxide films deposited by radio frequency plasma enhanced chemical vapor deposition method: Optical and structural properties

Silicon rich silicon oxide films have been deposited by plasma enhanced chemical vapour deposition using a gas mixture of silane, carbon-di-oxide and hydrogen. Silicon nanocrystals formations in the as deposited silicon rich silicon oxide films have been detected by high resolution transmission electron microscopy, scanning electron microscopy, Raman scattering and X-ray diffraction studies. Structural changes under different deposition condition have been studied by Fourier transform infrared spectroscopy. The oxygen and hydrogen bonding configurations have been obtained from Fourier transform infrared spectroscopy. Room temperature photoluminescence spectra have been observed for the as deposited films. The structural properties together with photoluminescence spectra allowed us to gain insight about the Si nanocrystal formation.     

基于中红外光声光谱的聚合物包膜控释肥料养分释放曲线预测

以聚丙烯酸酯类系列水基聚合物包膜控释肥料为样品,测定了包膜肥料养分的释放曲线并原位测定了肥料包膜的中红外光声光谱,分析了不同肥料的养分释放曲线以及不同包膜材料的红外光声光谱特征;采用广义回归神经网络模型(GRNN),以肥料包膜红外光声光谱的主成分作为GRNN模型的输入层,并以包膜肥料养分释放曲线为输出层,构建了预测养分释放曲线的GRNN模型。结果表明,GRNN模型能快速有效地预测包膜肥料养分释放曲线,其预测相关系数(R2)达0.93以上;包膜的探测深度明显影响释放曲线的预测误差,最小预测误差为7.14%,平均为10.28%,且基于包膜表层红外光声光谱的预测误差最小。因此,结合GRNN模型,红外光声光谱可为包膜肥料养分释放曲线的快速预测提供新手段。     

Pulsed photoacoustic technique to measure the absorption coefficients of the highly transparent optical materials

A new technique of measuring the low optical absorption coefficient is described by using pulsed photoacoustic calorimetry. The frequency dependence of the photoacoustic signal is different owing to its main origin, either the bulk absorption or the surface absorption. The Fourier transform of the pulsed photoacoustic signal, generated by a pulsed CO₂ laser, is obtained as the frequency response of the photoacoustic signal. The ratio of the bulk absorption coefficient and surface absorption coefficient is acquired as 1:1.5.     

Adsorption of biodegradable chelating compounds on inorganic oxides

The Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) method to characterize the interactions between selected aminopolycarboxylic acids and inorganic oxides surfaces is reviewed. In this work, the adsorption of four aminopolycarboxylates (biodegradable and with augmented biodegradability; all in the form of sodium salts), viz. ethylenediaminedisuccinic (EDDS), diethylenetriaminepentaacetic (DTPA), N-(hydroxyethyl)ethylenediaminetriacetic (HEDTA) and methylglycinediacetic (MGDA) acids on: zirconia, titania and alumina was carried out. The obtained results differ depending on the kind of aminopolycarboxylic acid used and the type of oxide support adsorbent characterized by its pH_PZC value.     

Remote Fourier Transform Infrared Emission Spectroscopy in the Studies of the Solid Propellant Combustions

In this paper infrared emission spectra of the solid propellant combustion using remote Fourier transform spectroscopy have been studied. Both the infrared spectral radiance distributions and gas quantitative method for solid propellant combustions by remote Fourier transform infrared emission spectroscopy have been presented. In the method we utilize estimating temperature measuring models, which are modified by Junde Wang, based on emission fundamental band measurements of HCl or HF. Through measuring the temperature both the infrared spectral radiance distributions of the solid propellant combustions and their emisivities can be obtained. A remote measured gas concentration model based on combustion temperature, spectral radiance and emissivity has been developed. Field single-ended measurements at long distances for solid propellant plumes at temperature 1700—3500K can be extended to measuring fluctuations of instantaneous temperature and combustion reaction products.     

Detection of lethal fake liquors using digitally labelled gas-phase Fourier transform infrared spectroscopy

Fake liquors have caused severe body injuries or even deaths worldwide, rapid detection of such lethal drinks is thus quite necessary. Methanol has been identified as a primary cause of the problem, so methanol monitoring is critical to the detection of fake liquors. The present work provides an effective strategy for rapid detection of different lethal fake liquors. Using gas-phase Fourier transform infrared spectroscopy in a digitally labeled approach, the spectral bands of methanol were extracted by the iterative discrete wavelet transform for classification, which is named as digitally labeled gas-phase Fourier transform infrared spectroscopy. In digitally labeled gas-phase Fourier transform infrared spectroscopy, principal component analysis and least square support vector machine were combined to discriminate problematic samples using the iterative discrete wavelet transform filtered signals. As a result, the method could cleverly extract spectral features of methanol from the alcoholic drinks in the presence of uncontrolled matrix effects. The recognition accuracy was higher than 97.0%, and each measurement was done within 3?min. The results illustrate that the digitally labeled gas-phase Fourier transform infrared spectroscopy method serves well to rapidly discriminate fake liquors as an efficient and promising tool, and could be well extended to detection of any other targeted volatile substance in complicated systems.     

Photoacoustic infrared spectroscopic studies of silica gels with organically functionalized surface

The article shows the application of photoacoustic Fourier transform infrared spectroscopy as a tool for identification of signal characteristics of organic ligands immobilized at the silica gel. Each of the compounds studied had an alkyl chain. Therefore, the differences could be observed on the basis of the position (wavenumbers) and appearance of bands typical of the carbon–hydrogen stretching vibrations. However, an important observation was that depending on the organic unit at the silica surface, it was possible to easily distinguish between signals specific to the ligand. The only exception was the system with functional groups whose signals coincided with the bands typical of inorganic silica.     

Absolute line intensities in the ν1 + 3ν3 band of 12C2H2 by laser photoacoustic spectroscopy and Fourier transform spectroscopy

Line intensities and self-broadening coefficients in the ν₁ + 3ν₃ band of ¹²C₂H₂ near 0.8 μm at room temperature were measured by means of both laser photoacoustic and Fourier transform spectroscopy. An experimental protocol has been developed to obtain absolute intensities from the photoacoustic measurements. Namely, the spectrometer was calibrated using water vapour line intensities available in Hitran 1996 [L. S. Rothman et al. (1998) J. quant. Spectrosc. Radiat. Transfer, 60, 665–710]. These photoacoustic line intensities were found to be on average 5% higher than corresponding measurements performed using Fourier transform spectroscopy, the accuracy of the latter being estimated to better than 4%. The accuracy of the photoacoustic intensities is discussed. Previous results from the literature [F. Herregodts, D. Hurtmans, J. Vander Auwera, and M. Herman (1999) J. chem. Phys., 111, 7954—7960] are revised.