Far infrared emission spectra from stratospheric hydrogen peroxide

Synthetic emission spectra from two stratospheric altitude observations have been analyzed for the presence of H₂O₂ in the far infrared region. The calculations are made with a high spectral resolution (10^–3 cm^–1 or 10^–4 cm^–1) greater than those in experimental measurements which are in the region of 3.10^–3 cm^–1. Spectra cover a spectral interval between 40 and 120 cm^–1 showing the best features of H₂O₂ susceptible to observation in a stratospheric spectrum. The optimum conditions for identification have been considered. Using the variations in H₂O₂ abundance in the measurement data and photochemical models, the H₂O₂ features detection limits have been studied.     

Fourier-transform infrared emission spectroscopy of BO

The Fourier-transform infrared emission spectra of BO were recorded using a Bruker IFS 125 HR spectrometer. The observed spectrum of BO in the 1200-2100 cm⁻¹ region contains three bands: the fundamental bands of ¹¹BO and ¹⁰BO and a hot band of ¹¹BO with band origins measured to be 1861.9242(97), 1915.3071(09) and 1838.3773(68) cm⁻¹, respectively.     

Ultrafast nonequilibrium Fourier-transform two-dimensional infrared spectroscopy

We present what we believe to be the first implementation of nonequilibrium two-dimensional IR spectroscopy (2DIR) combining electronic excitation within the Fourier transform (FT) approach. Nonequilibrium 2DIR spectra of Mn2(CO)10 and its photoproducts are obtained in two modalities: photoexcitation at 400 nm, either before a 2DIR probe or during the waiting time of the FT 2DIR measurement. Extending FT 2DIR to nonequilibrium systems offers insight into complex condensed-phase reaction dynamics.     

Active phase stabilization in Fourier-transform two-dimensional infrared spectroscopy

A scheme for active phase stabilization and absolute positioning in Fourier-transform two-dimensional (2D) IR spectroscopy is presented. The position accuracy is better than 20 nm(rms) corresponding to lambda/250 at 5 microm, which significantly improves the quality of Fourier-transform 2D IR spectra. Phase stabilization is added to a standard photon echo setup in a way that does not impair the flexibility of the experiment and the control over IR pulse parameters.     

Far infrared laser thermal spectroscopy of superconductors

An optically pumped far infrared laser provides fixed photon energies near the superconducting gap, making it possible to carry out experiments where the temperature is swept through T_c. Such thermal measurements in thin films of V₃Si show both known and unexplained features, with some of the latter perhaps due to a second gap. The thermal technique shows potential for the study of superconductors.Work supported by the U.S. Department of Energy under Contract No. DE-AS05-79ER10436.     

Fourier-transform infrared derivative spectroscopy with an improved signal-to-noise ratio

Infrared derivative spectroscopy is a useful technique for finding peaks hidden in broad spectral features. A data acquisition technique is shown that will improve the signal-to-noise ratio (SNR) of Fourier-transform infrared (FTIR) derivative spectroscopy. Typically, in a FTIR measurement one samples each point for the same time interval. The effect of using a graded time interval is studied. The simulations presented show that the SNR of first-derivative FTIR spectroscopy will improve by 15% and that the SNR of second-derivative FTIR will improve by 34%.     

Dispersive Fourier-transform spectroscopy of surface plasmons in the infrared frequency range

The optical scheme and the principle of operation of an asymmetric Mach-Zehnder interferometer for dispersive spectroscopy of surface IR plasmons are discussed. A thin-layer sample deposited on a conducting substrate, which guides surface plasmons, is placed in one of the arms of the interferometer. This makes it possible, by applying a complete Fourier transform to the interferogram, to obtain the spectrum of the complex refractive index of surface plasmons and, therefore, of the complex dielectric permittivity of the sample or the substrate material.     

红外光谱结合主成分分析鉴别不同产地黄柏

利用傅里叶变换红外光谱仪收集6个不同产地黄柏的红外光谱,原始光谱经过多点基线校正、五点平滑预处理后,统计各个产地黄柏的平均光谱,结果显示,6个产地黄柏的平均红外光谱整体上相似;在指纹特征区域1 800～500cm-1,选取经过归一化的红外光谱,建立主成分分析鉴别模型.建模结果表明,三个主成分能代表98%的指纹区变量信息,样本在主成分空间中聚集成为不同的类别,基本实现不同产地黄柏的鉴别,此外,在一定程度上,样本分布疏密度反映样本的亲缘关系.提取模型的载荷因子,分析显示,6个产地黄柏的差异主要在蛋白质、糖类、脂类、生物碱类、黄柏甾醇类、黄柏内酯、黄柏酮、黄柏酮酸八种物质成分上体现.因此,红外光谱结合主成分分析法可以快速、无损地鉴别不同产地黄柏,并且能反映不同产地黄柏物质成分含量的差异.     

A Study of ibuprofen solubility in supercritical carbon dioxide by Fourier-transform infrared spectroscopy

In the work, a method of study of solubility of pharmaceutical substances in high-pressure gases and supercritical media with Fourier-transform IR spectroscopy has been developed. An investigation of the process of ibuprofen dissolution in supercritical carbon dioxide (SC CO₂) in a real-time scale has been performed. On the basis of analysis of the time dependences of the integral intensities of the selected IR-absorption bands of ibuprofen on the value of the initial weighed portion the value of solubility (molar fraction) of ibuprofen in SC CO₂ at a temperature of 35°C and pressure of 15.0 MPa was obtained, being equal to (8.9 ± 1.6) × 10^?3.     

Far infrared spectroscopy of praseodymium magnesium nitrate using a polarizing interferometer

A number of contradictions exist in the published far i.r. spectra of praseodymium magnesium nitrate. Spectra recorded with improved spectrophotometric accuracy with a polarizing interferometer have enabled these to be resolved. Transitions from the ground doublet to the first excited singlet state of the Pr³⁺ ion showed no evidence of the small ground state splitting. The Zeeman splitting of this absorption is as predicted from the ground stateg-value but the components are of unequal width. Other features of the spectrum are described.     

Compact frequency-comb Fourier-transform infrared spectrometer

We demonstrate a Fourier-transform infrared (FTIR) spectrometer without moving parts based on frequency-combs where the interference of two coherent frequency-comb beams occurs via wavefront combination, thereby eliminating the need of a dielectric combiner. This enables dispersionless operation over eventually the complete THz-to-visible spectrum in a single instrument. Furthermore we demonstrate the use of a single GaSe crystal for generating both beams, in an implementation for the 22-36 THz mid-infrared range. Spurious cross-modulation effects and a way to eliminate them are experimentally demonstrated. The compact comb-FTIR can be equally well applied for spectroscopic microscopy as for long-path standoff chemical monitoring.     

Visible-infrared two-dimensional Fourier-transform spectroscopy

We report on a new class of optical multidimensional Fourier-transform spectroscopy associated with a visible excitation-infrared emission configuration, in which the emitted field results from second-order optical nonlinearities. This configuration is demonstrated on a phase-matched sample of known nonlinear response by coherent measurement of the mid-infrared field emitted after a femtosecond visible double-pulse excitation.     

Multidimensional quantum dynamics and infrared spectroscopy of hydrogen bonds

Hydrogen bonds are of outstanding importance for many processes in Chemistry, Biology, and Physics. From the theoretical perspective the small mass of the proton in a hydrogen bond makes it the primary quantum nucleus and the phenomena one expects to surface in a particular clear way are, for instance, zero-point energy effects, quantum tunneling, or coherent wave packet dynamics. While this is well established in the limit of one-dimensional motion, the details of the multidimensional aspects of the dynamics of hydrogen bonds are just becoming accessible to experiments and numerical simulations.     

Fourier-transform spectroscopy using liquid-crystal technology

We report the use of a ferroelectric liquid-crystal (FLC) mask as an optical encoder for development of a solid-state Fourier-transform spectrometer. For this demonstration a 1x64 element array was striped and used as a 1x4 element device. The device intersected dispersed radiation and encoded each spectral component with a carrier signal by applying half-wave potential to each of the four striped (1x16) FLC elements, which varied the transmitted amplitude of the light from 0.03% to 28% of full scale. The light was spectrally recombined and imaged onto a photomultiplier and the resulting carriers (and their amplitudes) detected by Fourier transformation of the time-varying signal. Spectra of colored-glass filters were taken to demonstrate the possibilities of the instrument.     

Far infrared heterodyne detectors

The characteristics of far infrared detectors are reviewed. Three detectors, the InSb hot electron bolometer, the GaAs Schottky diode and the Josephson point contact junction, have been incorporated as mixers into sensitive heterodyne systems. The performances of existing heterodyne receivers/radiometers are described and compared. Other applications of submillimeter heterodyne techniques are discussed.Supported in part by the U. S. Army Research Office and the Department of the Air Force.     

Far infrared absorption of a-GeSe

Far infrared absorption measurements have been made on a series of a-Ge_xSe_1?x films with near equiatomic compositions. The only sharp feature is an absorption line at 260cm^-1, and the compositional dependance of this feature is correctly described by a model in which the Ge(Se) atoms are 4(2) fold co-ordinated. There is no evidence in our amorphous samples of any absorption band in the frequency range (160?190cm^?1) of the major IR active modes of 3:3 fold co-ordinated crystalline GeSe.