Infrared microspectroscopy station at BL43IR of SPring-8

BL43IR of SPring-8 has been constructed for the infrared materials researches, and it covers a wide spectral range from 100 to 20,000 cm⁻¹. The microspectroscopy station of this BL has a spatial resolution smaller than 10 μm in diameter in the mid-infrared region without apertures. This station had been mainly used within mid-infrared region, and its performance in the far-infrared region had not been tested. In this paper, we examined the capability of the microscope in the far-infrared region and the spatial resolution is found to be almost at the diffraction limit. The microspectroscopy station has been revealed to have a good performance for doing materials researches in all the spectral range available.     

BL43IR at SPring-8 redirected

BL43IR at SPring-8 is overviewed regarding the beamline properties on the flux, the brilliance and the noise in comparison with the conventional thermal radiation (TR). The flux is comparable to the TR, and what makes the most of BL43IR is to utilize the high brilliance. We redirect our strategy to concentrate on the microscopes with highly brilliant infrared radiation from SPring-8 and attract the vast TR spectroscopy community.     

Infrared facility at the Canadian light source

The Canadian Light Source (CLS) is constructing two beamlines for Infrared Spectroscopy using synchrotron radiation (IRSR). One will supply mid-Infrared (2–25 μ) light to a Fourier Transform Infrared (FTIR) spectrometer and microscope for biological applications. The second will have a high resolution FTIR spectrometer for gas-phase and surface spectroscopy in the far-Infrared (beyond 25 μ). The Infrared beamlines will use dipole bending magnet radiation from a special bend magnet port design which provides a 50 mrad square acceptance. Issues with the first mirror and photon mask design, as well as the beamline layout and features are discussed.     

High pressure X-ray emission spectroscopy at the advanced photon source

ABSTRACT

The structural, electronic, and magnetic properties of materials under high pressure are of fundamental interest in physics, chemistry, materials science, and earth sciences. Among several hard X-ray-based techniques, X-ray emission spectroscopy (XES) provides a powerful tool to probe element-specific information for understanding the electronic and magnetic properties of materials under high pressure. Here, we discuss on the particular requirements and instrumentation used in high pressure XES experiments. We then present several examples to illustrate the recent progress in high pressure XES studies at the Advanced Photon Source, followed by an outlook toward future development in high pressure XES.     

High-resolution far-infrared spectroscopy at NSLS beamline U12IR

A Bruker model IFS 125HR Fourier transform interferometer has been installed and its performance tested using high-brightness, far-infrared synchrotron radiation. Results of absorption measurements for the rotational modes of water vapor demonstrate a nearly 10-fold improvement in signal-to-noise when compared with the instrument’s internal high-pressure Hg arc lamp source.     

Frontiers in infrared spectroscopy at surfaces and interfaces

An overview of advances in infrared (IR) spectroscopy is presented. Recent results in several areas of topical interest, including examples in biocompatibility, dielectric films, in situ chemical reactions, and electron relaxation in nanoparticles, are highlighted. Major advances in IR experimental methods include the development of accelerator-based sources of IR light and the application of novel techniques to examine complex systems. These advances, and their role in elucidating crucial insights about surfaces and interfaces, are illustrated by recent work in the literature. After reviewing the current state of the art, promising future directions are discussed. In particular, superb opportunities are expected to develop in a broad range of scientific disciplines, e.g., biology, device engineering, chemistry, and physics.     

Time‐resolved photoelectron spectroscopy using synchrotron radiation time structure

Synchrotron radiation time structure is becoming a common tool for studying dynamic properties of materials. The main limitation is often the wide time domain the user would like to access with pump–probe experiments. In order to perform photoelectron spectroscopy experiments over time scales from milliseconds to picoseconds it is mandatory to measure the time at which each measured photoelectron was created. For this reason the usual CCD camera‐based two‐dimensional detection of electron energy analyzers has been replaced by a new delay‐line detector adapted to the time structure of the SOLEIL synchrotron radiation source. The new two‐dimensional delay‐line detector has a time resolution of 5 ns and was installed on a Scienta SES 2002 electron energy analyzer. The first application has been to characterize the time of flight of the photoemitted electrons as a function of their kinetic energy and the selected pass energy. By repeating the experiment as a function of the available pass energy and of the kinetic energy, a complete characterization of the analyzer behaviour in the time domain has been obtained. Even for kinetic energies as low as 10 eV at 2 eV pass energy, the time spread of the detected electrons is lower than 140 ns. These results and the time structure of the SOLEIL filling modes assure the possibility of performing pump–probe photoelectron spectroscopy experiments with the time resolution given by the SOLEIL pulse width, the best performance of the beamline and of the experimental station.     

High-resolution infrared spectroscopy of NNO and NNO in the 1200–3500 cm region

We present a continuation of our investigation of the second most abundant isotopic species of nitrous oxide, ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O, in the infrared (IR). Our two previous contributions looked at the 3500–9000 cm⁻¹ region for ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O, respectively, in the 3500–9000 cm⁻¹ region. The use of highly enriched isotopologue samples in this study allowed us to go further into the IR, down to 1200 cm⁻¹. A total of 2 2742 transitions have been assigned based on the effective Hamiltonian model, with 108 of them being reported here for the first time. Rovibrational analyses of 98, 101, 8, 3, 6, 1 and 1 bands for the ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O, ¹⁵N¹⁵N¹⁶O, ¹⁴N¹⁵N¹⁸O, ¹⁵N¹⁴N¹⁸O, ¹⁴N¹⁵N¹⁷O and ¹⁵N¹⁴N¹⁷O isotopologues, respectively, were also performed.     

Angle-dependent infrared absorption spectroscopy at electrode/electrolyte interfaces

Angle-dependent internal reflection spectroscopy is performed in the attenuated total reflection setup for an electrochemical cell with a Fourier transform infrared spectrometer. The working electrode is a thin Pt film evaporated onto a hemispherical Si prism. The refractive index of the Pt film obtained from the experiment is found to differ from the value for bulk material. The difference is ascribed to the surface corrugation of the Pt surface and the film thickness in the nanometer range. The function of reflection intensity versus angle of incidence changes significantly when a resonant absorption occurs in the electrolyte medium. The angle-dependent absorption band intensity of CO adsorbed on the Pt film under potential control reveals changes in magnitude and an inversion of the band for different angles of incidence. This behaviour is explained by the excitation of resonant surface plasmon waves at the Pt/electrolyte interface and by multiple reflections occurring at the interfaces. A simulation for the three-layer system Si/Pt/electrolyte agrees with the experimental results.     

Design and construction of a compact end-station at NSRRC for circular-dichroism spectra in the vacuum-ultraviolet region

A synchrotron‐radiation‐based circular‐dichroism end‐station has been implemented at beamline BL04B at the National Synchrotron Radiation Research Center (NSRRC) in Taiwan for biological research. The design and performance of this compact end‐station for measuring circular‐dichroism spectra in the vacuum‐ultraviolet region are described. The linearly polarized light from the beamline is converted to modulated circularly polarized light with a LiF photoelastic modulator to provide a usable wavelength region of 130–330 nm. The light spot at the sample position is 5 mm × 5 mm at a slit width of 300 µm and provides a flux greater than 1 × 10¹¹ photons s^?1 (0.1% bandwidth)^?1. A vacuum‐compatible cell made of two CaF₂ windows has a variable path length from 1.3 µm to 1 mm and a temperature range of 253–363 K. Measured CD spectra of (1S)‐(+)‐10‐camphorsulfonic acid and proteins demonstrated the ability of this system to extend the wavelength down to 172 nm in aqueous solution and 153 nm in hexafluoro‐2‐propanol.     

X-ray diffraction and infrared spectroscopy of monazite-structured CaSO4 at high pressures: Implications for shocked anhydrite

X-ray diffraction and infrared spectroscopy of CaSO₄ are conducted to pressures of 28 and 25 GPa, respectively. A reversible phase transition to the monoclinic monazite-structure occurs gradually between 2 and ∼5 GPa with a highly pressure-dependent volume change of ∼6-8%. A second-order fit of the X-ray data to the Birch-Murnaghan equation of state yields a bulk modulus (K) of 151.2 (±21.4) GPa for the high-pressure monoclinic phase. In the high-pressure infrared spectrum, the infrared-active asymmetric stretching and bending vibrations of the sulfate tetrahedra split at the phase transition, in accord with the results of factor group analysis. Additionally, the tetrahedral symmetric stretching vibration, which is weak in the anhydrite phase, becomes strongly resolved at the transition to the monazite structure. The infrared results indicate that the sulfate tetrahedra are more distorted in the monazite-structured phase than in anhydrite. Kinetic calculations indicate that the anhydrite to monazite transformation may generate the phase transition observed near 30 GPa under shock loading in CaSO₄. Our results indicate that the anhydrite- and monazite-structured phases may be the only phases that occur under shock loading of CaSO₄ to pressures in excess of 100 GPa.     

Doppler-limited CW infrared cavity ringdown spectroscopy of the ν1+ν3 OH + CH stretch combination band of jet-cooled methanol

A high resolution cavity ringdown spectrometer (CRDS) has been constructed using a 1.5 μm continuous-wave external-cavity tunable diode laser, a mode-matched near-confocal ringdown cavity, and 2 cm pulsed slit jet. Without signal averaging, the RMS noise in the absorption signal is 1.7 × 10⁻⁹ cm⁻¹. The rotationally resolved overtone spectrum of the OH(ν₁) + CH(ν₃) stretch combination band of methanol between 6510 and 6550 cm⁻¹ has been observed for J^′=0-8 and K^′=0-3 at sub-Doppler resolution. In total, 418 lines are assigned and global fits yield molecular torsion-rotation parameters for the upper state. Four K^′-localized perturbations are analyzed and the pattern of residuals is discussed.     

Quantitative measurement of integrated band intensities of benzene vapor in the mid-infrared at 278, 298, and 323 K

Pressure broadened (1 atm. N₂) laboratory spectra of benzene vapor (in natural abundance) were recorded at 278, 298, and 323 K, covering 600-6500 cm⁻¹. The spectra were recorded at a resolution of 0.112 cm⁻¹ using a commercial Fourier transform spectrometer. The pressure of each benzene vapor sample was measured using high-precision capacitance manometers, and a minimum of nine sample pressures were recorded for each temperature. The samples were introduced into a temperature-stabilized static cell (19.94(1) cm pathlength) that was hard-mounted into the spectrometer. From these data a fit composite spectrum was calculated for each temperature. The number density for the three composite spectra was normalized to 296 K. The spectra give the absorption coefficient (cm² molecule⁻¹, naperian units) as a function of wavenumber. From these spectra integrated band intensities (cm molecule⁻¹ and atm⁻¹ cm⁻²) for intervals corresponding to the stronger benzene bands were calculated and were compared with previously reported values. We discuss and quantify error sources and estimate our systematic (NIST Type-B) errors to be 3% for the stronger bands. The measured absorption coefficients and integrated band intensities are useful for remote sensing applications such as measurements of planetary atmospheres and assessment of the environmental impact of terrestrial oil fire emissions.     

Temperature dependence of the absorption spectrum of CH4 by high resolution spectroscopy at 81 K: (I) The region of the 2ν3 band at 1.66 μm

In a recent contribution, (Gao B, Kassi S, Campargue A. Empirical low energy values for methane transitions in the 5852-6181 cm⁻¹ region by absorption spectroscopy at 81 K. J Mol Spectrosc 2009;253:55-63.), the low energy values of methane transitions between 1.71 and 1.62 μm were derived from the variation of the line intensities between 296 and 81 K. The line intensities at 81 K were retrieved from the high resolution absorption spectrum of methane recorded at liquid nitrogen temperature by direct absorption spectroscopy using a cryogenic cell and a series of distributed feed back (DFB) diode lasers. For the line intensities at 296 K, the values provided by the HITRAN database were used. As a consequence of the relatively high intensity cut off (4×10⁻²⁴ cm/molecule) of the HITRAN line list in the considered region, the lower energy values were derived for only 845 of the 2187 transitions measured at 81 K. In the present work, our line list was extended by the retrieval of many weak line intensities leading to a set of 3251 transitions. The minimum value of the measured line intensities (at 81 K) is on the order of 10⁻²⁶ cm/molecule. In relation with the project “Greenhouse Gases Observing Satellite” (GOSAT), a much more complete line list for CH₄ at 296 K has become available (intensity cut off of 4×10⁻²⁶ cm/molecule). By applying the two temperature method to our line intensities at 81 K and GOSAT intensities at 296 K, the lower energy values of 2297 transitions could be derived. These transitions represent 99.1% and 90.8% of the total absorbance in the region, at 81 and 296 K respectively. This line list provided as Supplementary Material allows then accounting for the temperature dependence of CH₄ absorption below 300 K. The investigated spectral range is dominated by the 2ν₃ band near 6005 cm⁻¹ which is of particular interest for atmospheric retrievals. The factor 2 narrowing of the Doppler linewidth from room temperature down to 81 K has allowed the resolution of a number of 2ν₃ multiplets and improving the line intensity retrievals. A detailed comparison with GOSAT and HITRAN line lists has revealed a number of possible improvements.