Far infrared laser lines and assignments of CH3OH: a review

Methyl alcohol is the most important lasing molecule in the Far-Infrared (FIR) spectral region, and the most widely used for investigation and for applications. Since the last critical review of 1984, over seventy papers have been published dealing with the FIR laser lines and the infrared spectroscopy of CH₃OH. In 1984 we could list about 330 FIR laser lines, 98 of which were measured in frequency and 105 assigned. Since then more than 70 papers were published increasing the number of the known laser lines to 575 (103 measured in frequency). Also the FIR and IR spectroscopy was largely improved thanks to the analysis of high resolution FT spectra, and the number of the correctly assigned laser lines has been increased to 224. The wavenumbers of the assigned lines can now be predicted with an accuracy of about 0.001 cm^–1 or better, thus approaching the accuracy of the experimental frequency measurements.     

The Vibrational Spectra and Normal Coordinate Analysis of Semiconducting Y2BaCuO5

Both infrared (FTIR) and Raman spectra have been measured for the green semiconducting Y₂BaCuO₅ (2:1:1) in the Y-Ba-Cu-O system. Factor group analysis and normal-coordinate-analysis calculations have been conducted for this phase in order to determine the symmetries, the wavenumber locations and the eigenvector nature of its first-order modes of vibration along with the appropriate set of modified GVF force constants. The predicted vibrational spectral results are in good agreement with the experimentally observed FTIR and Raman spectral data. The generated force constants are interpreted along with those for related phases on the basis of structure.     

The 1.58 μm transparency window of methane (6165-6750 cm): Empirical line list and temperature dependence between 80 and 296 K

The empirical line parameters of over 12,000 methane transitions have been obtained at 80 K in the 1.58 μm transparency window (6165-6750 cm⁻¹) which is of importance for planetary applications. This line list (WKC-80K) was constructed from high sensitivity spectra of normal abundance methane recorded by CW-Cavity Ring Down Spectroscopy at low temperature. The minimum intensity reported is on the order of 5×10⁻³⁰ cm/molecule. High resolution Fourier transform spectra have also been recorded using enriched CH₃D samples at 90-120 K in order to facilitate identification of monodeuterated methane features in the methane line list at 80 K. The CH₃D relative contribution in the considered region is observed to be much larger at 80 K than at room temperature. In particular, CH₃D is found dominant in a narrow spectral window near 6300 cm⁻¹ corresponding to the highest transparency region.Using a similar line list constructed at room temperature (Campargue A, Wang L, Liu AW, Hu SM and Kassi S. Empirical line parameters of methane in the 1.63-1.48 μm transparency window by high sensitivity Cavity Ring Down Spectroscopy. Chem Phys 2010;373:203-10.), the low energy values of the transitions observed both at 80 K and at room temperature were derived from the variation of their line intensities. Empirical lower states and J-values have been obtained for 5671 CH₄ and 1572 CH₃D transitions representing the most part of the absorbance in the region. The good quality of these derived energy values is demonstrated by the marked propensity of the corresponding CH₄ lower state J values to be close to integers. The WKC line lists at 80 K and room temperature provided as Supplementary Material allow one accounting for the temperature dependence of methane absorption between these two temperatures. The importance of the 80 K line list for the study of Titan and other methane containing planetary atmospheres is underlined and further improvements are proposed. The resulting information will advance the theoretical modeling of the methane spectrum in the 1.58 μm transparency window.     

Surface Acidity of H-Birnessite: Infrared Spectroscopic Study of Formic Acid Decomposition

This paper presents the adsorption and thermal decomposition mechanism of formic acid on an H-birnessite sample. Changes in the surface and structure were characterized using infrared spectroscopy, N₂ gas adsorption–desorption, and thermal analysis techniques. The acid sites of H-birnessite were investigated by infrared and thermal analysis using pyridine as a molecular probe. Decomposition of formic acid started on H-birnessite at 120°C and was complete at 400°C. Infrared spectra revealed that the molecularly adsorbed formic acid species were transformed to a formate species, and the formate species were transformed to CO. The most stable adsorption structure for formic acid was found as a molecular monodentate configuration.     

中红外光纤技术用于腮腺肿瘤诊断的研究

采用傅里叶变换红外光谱法与中红外光导纤维联用技术对１１例肿瘤，７例正常腮腺和１例舍格伦综合症的红外光谱进行了对比研究。结果发现正常腮腺和舍格伦综合症的红外光谱很相似，而与肿瘤的光谱存在着明显差别，同时也观察到良性与恶性肿瘤的光谱在若干波段处也有所不同．     

1H NMR Spectral Simplification with Achiral and Chiral Lanthanide Shift Reagents. Paramethadione, 5-Ethyl-3,5-Dimethyl-2,4-Oxazolidinedione

Abstract

The 60 MHz ¹H NMR spectra of paramethadione, 5-ethyl-3,5-dimethyl-2,4-oxazolidinedione, 1, have been studied at 28° in CDCl₃ solution with the achiral reagent tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium(III), 2, and the chiral reagents tris[3-(trifluoromethylhydroxymethylene)?(+)-camphorato]europium(III), 3, and tris[3?(heptafluoropropylhydroxymethylene)?(+)-camphorato]europium(III), 4.SubstantiaΔδ values and spectral simplification are achieved with 2 or 4. Significant enatiomeric shift differences, ΔΔδ, are observed with 4 that should provide direct optical purity determinations of ? 1, using the C(5)CH3 or the NCH, signals with &;:Iratios of 1.3–1.5. Valley height for the CCH, resonance as low as 4.8% was achieved, which should allow detection of as little as 3–4% of the minor enantiomer. Results are discussed in terms of the structural features of I and of the LSR. Substantial nb values and spectral simplification     

The Infrared and Raman Spectra of β-and α-Tricalcium Phosphate (Ca3(Po4)2)

Factor group analysis was applied to interpret the vibrational spectra of β-and α-tricalcium phosphate (Ca₃(PO₄)₂). The analysis predicts the number of bands formed due to the splitting of the fundamental vibrational modes of the PO₄ ^3-ion. The number of the infrared and Raman bands predicted by this analysis for the two phases are drastically different and can be ascribed to the difference in atomic arrangements in the two phases resulting in greater shielding of the PO₄ ^3-ions in the β-phase than in the α-phase. Discrepancies in the number of predicted and experimentally-observed bands can be attributed to the weak intensities of some vibrational modes or the convolution of vibrations and limited spectral resolution.     

Infrared absorption cross-sections for acetaldehyde (CH3CHO) in the 3 μm region

A series of infrared absorption cross-sections for acetaldehyde has been measured in the 3 μm region from spectra obtained using a high-resolution Fourier transform spectrometer (Bruker IFS 125/HR). Results presented are for mixtures of acetaldehyde vapor combined with pure synthetic air taken at various temperatures and pressure to simulate atmospheric conditions found principally in the Earth's troposphere and lower stratosphere. Spectra were recorded at a resolution of 0.005 cm⁻¹ and intensities were calibrated using three acetaldehyde spectra (measured at 278, 298 and 323 K) provided by the Pacific Northwest National Laboratory (PNNL) IR database.     

CH4-Ne体系的三维从头算势能面与光谱的模拟

本文在从头算CCSD(T)/AVXZ(X=T,Q)水平上计算了CH₄-Ne体系的三维势能面,同时在基组中加入了键函数,并且将基组外推到完全基组极限水平. 通过最小二乘法拟合摩斯长程势能函数形式,获得了三维分析势能面,其中对664个从头算格点的拟合的标准偏差仅为0.042 cm^-1. 随后,采用径向离散变量表象和角度有限基组表象相结合的杂化基函数方法,并基于Lanzcos迭代的方法获得了CH₄-Ne体系的振转能级,所预测的红外光谱与实验值非常吻合. 本文首次给出了CH₄-Ne体系的微波光谱数据. CH₄-Ne体系三维摩斯长程势能面分析的表达式为今后CH₄在Ne团簇动力学性质以及其碰撞诱导吸收光谱的研究中奠定了基础.     

Terahertz absorption spectra of nitromethane

Nitromethane, with its heavy frame and internal rotator, readily evaporates into the atmosphere making it an ideal candidate for remote sensing. Here we present the absorption spectra of gas-phase nitromethane between 9 and 50 cm⁻¹. Measurements were taken using a Bruker IFS 66v Fourier transform far-infrared (FTIR) spectrometer at a resolution of 0.12 cm⁻¹ (0.0036 THz) from 9 to 40 cm⁻¹ and a Bruker Vertex 80v FTIR spectrometer with a resolution of 0.0075 cm⁻¹ (0.00226 THz) from 10 to 50 cm⁻¹. The absorption spectra were measured at multiple pathlengths ranging from 2 to 6 m. These measurements were used to calculate the absorption coefficient of nitromethane as a function of wavenumber.     

Raman and Infrared Spectra of Matrix Isolated CO2 and CS2

The matrix isolation infrared and Raman spectra of CO₂ and CS₂ in solid krypton at 20°K are reported. The fundamental frequencies are only very slightly red-shifted from the free gas values. Isotopic effects are found in both infrared and Raman spectra, whereas site splittings are evident in the infrared only.     

Solvothermal synthesis and characterization of α-Fe2O3 nanodiscs and Mn3O4 nanoparticles with 1,10-phenanthroline

α-Fe₂O₃ nanodiscs and Mn₃O₄ nanoparticles have been prepared by the 1,10-phenanthroline as complexing agent in the presence of sodium hydroxide under hydrothermal conditions. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectra. The average diameter of α-Fe₂O₃ nanodiscs is of 2 μm. In the case of Mn₃O₄ sample, the Mn₃O₄ crystallites are nanoparticles with an average size of 34 nm. A formation mechanism for the α-Fe₂O₃ and Mn₃O₄ nanomaterials was proposed.     

微波等离子体化学气相沉积法制备C3N4薄膜的结构研究

采用微波等离子体化学气相沉积法,用高纯氮气(99.999%)和甲烷(99.9%)作反应气体,在单晶Si(100)基片上沉积C₃N₄薄膜.利用扫描电子显微镜观察薄膜形貌,表明薄膜由密排的六棱晶棒组成.X射线衍射和透射电子显微镜结构分析说明该薄膜主要由β-C₃N₄和α-C₃N₄组成,并且这些结果与α-C₃N₄相符合较好.由虎克定律近似关 关键词： 3N₄')" href="#">C₃N₄ 微波等离子体化学气相沉积法 薄膜沉积     

Anomalous energy loss distributions of alpha particles in heavily implanted thin aluminium films

Anomalous energy loss distributions of ^l48Gd alpha particles have been observed in heavily implanted thin aluminium films. It is surmised that thin film micro-wrinkling is responsible for the observed effect and that the novel technique of energy loss spectral analysis (ELSA) should be useful in studies of the topography of such films.     

Temperature dependence of the absorption spectrum of CH4 by high resolution spectroscopy at 81 K: (II) The icosad region (1.49-1.30 μm)

The high resolution absorption spectrum of methane has been recorded at liquid nitrogen temperature by differential absorption spectroscopy between 6717 and 7351 cm⁻¹ (1.49-1.36 μm) using a cryogenic cell and a series of distributed feed back (DFB) diode lasers. The investigated spectral region corresponds to the very congested low energy part of the icosad for which the HITRAN database provides neither rovibrational assignments nor the lower state energies. The positions and strengths at 81 K of 9389 transitions were obtained from the spectrum analysis. The minimum value of the measured line intensities (at 81 K) is on the order of 10⁻²⁶ cm/molecule. From the variation of the line strength between 81 K and 296 K, the low energy values of a total of 4646 transitions were determined. They represent 79.4% and 68.4% of the total absorbance in the region at 81 and 296 K, respectively, and include 28 transitions assigned to the ν₂+4ν₄ band near 6765 cm⁻¹. The reliability of the method based on the association of lines with coinciding centers in the 81 K and 296 K spectra is discussed. The results of the present analysis have been combined with previously analyzed high energy part of the icosad dominated by the ν₂+2ν₃ band near 7510 cm⁻¹. The line list for the whole icosad (6717-7655 cm⁻¹) consists of 12 865 transitions at 81 K.     

Infrared absorption cross sections for propane (C3H8) in the 3 μm region

Infrared absorption cross sections for propane have been measured in the 3 μm spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125 HR). The spectra of mixtures of propane with dry synthetic air were recorded at 0.015 cm⁻¹ resolution (calculated as 0.9/MOPD using the Bruker definition of resolution), at a number of temperatures and pressures appropriate for atmospheric conditions. Intensities were calibrated using two propane spectra (recorded at 278 and 293 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database.     

α-In2S3 and β-In2S3 phases produced by SILAR technique

In₂S₃ films have been deposited by the successive ionic adsorption and reaction technique (SILAR) at room temperature. The films have been examined to evaluate the structural and optical properties. X-ray diffraction spectra have revealed the presence of both the α-In₂S₃ (cubic) and β-In₂S₃ (tetragonal) phases. The presence of the α-In₂S₃ phase at room temperature is attributed to the richness of In in the deposited materials. The presence of both phases is also supported by FESEM observations. The crystallinity of the material has been observed to improve with increasing thickness. Direct band gap of the deposits decreased from 2.89 to 2.37?eV with increasing thickness.     

Visible Light Emission due to Resonant CO2 Laser Excitation of Dental Hard Tissue

Visible light emission of dental hard substances excited by high-power infrared pulses of a tunable TEA CO₂ laser has been investigated. A clear correlation between observed visible light emission, plasma formation as well as ablation of dental hard tissue has been demonstrated. Both, the highly nonlinear infrared to visible upconversion process and the ablation efficiency show a sharp spectral resonance close to a vibrational mode of PO₄ at 1090 cm^-1 in dental enamel and dentin. The influence of strong infrared light impulses on dental hard tissue is examined by performing upconversion studies of visible light emission of human dental enamel and dentin. Our experimental setup allows one to determine the plasma formation threshold being important in dental surgery.