Infrared Absorption Cross Sections Research Articles

Infrared absorption cross section of SiNx thin films

At the molecular level, resonant coupling of infrared radiation with oscillations of the electric dipole moment determines the absorption cross section, σ. The parameter σ relates the bond density to the total integrated absorption. In this work, σ was measured for the Si–N asymmetric stretch mode in SiNx thin films of varying composition and thickness. Thin films were deposited by low pressure chemical vapor deposition at 850 °C from mixtures of dichlorosilane and ammonia. σ for each film was determined from Fourier transform infrared spectroscopy and ellipsometric measurements. Increasing the silicon content from 0% to 25% volume fraction amorphous silicon led to increased optical absorption and a corresponding systematic increase in σ from 4.77 × 10−20 to 6.95 × 10−20 cm2, which is consistent with literature values. The authors believe that this trend is related to charge transfer induced structural changes in the basal SiNx tetrahedron as the volume fraction of amorphous silicon increases. Experimental σ values were used to calculate the effective dipole oscillating charge, q, for four films of varying composition. The authors find that q increases with increasing amorphous silicon content, indicating that compositional factors contribute to modulation of the Si–N dipole moment. Additionally, in the composition range investigated, the authors found that σ agrees favorably with trends observed in films deposited by plasma enhanced chemical vapor deposition.

Near infrared absorption cross sections for ethane broadened by hydrogen and nitrogen

Near infrared absorption spectra of ethane (C2H6) were recorded in the 1800–6200 cm−1 region by high resolution Fourier transform spectroscopy (Bruker IFS 125 HR) at the Canadian Light Source (CLS). Absorption cross sections were obtained for pure samples and with nitrogen or hydrogen as broadening gases as appropriate for astronomical environments. Corrections to the cross sections were made using data from the Pacific Northwest National Laboratory (PNNL) infrared database.

Erratum to “Infrared absorption cross sections of isobutane with hydrogen and nitrogen as broadening gases” J Quant Spectrosc Radiat Transf 227 (2019) 226–229

Erratum to “Infrared absorption cross sections of isobutane with hydrogen and nitrogen as broadening gases” J Quant Spectrosc Radiat Transf 227 (2019) 226–229

REPRINT OF: Infrared absorption cross-sections in HITRAN2016 and beyond: Expansion for climate, environment, and atmospheric applications

Spectroscopic analysis of hydrocarbons, halocarbons and related species is required in atmospheric applications such as climate-change research, tracking of pollution and biomass burning, and remote sensing. Critically evaluated line-by-line spectroscopic data are needed for such analyses. To address this need we report the large addition of spectra to the HITRAN2016 database. This extension increases the number of molecules in the database by almost a factor of 6 from that in HITRAN2012. Spectra from the Pacific Northwest National Laboratory database (Appl. Spectrosc. 2004;58:1452–61) and the Hodnebrog et al. compilation (Rev Geophys 2013;51:300–78) have been integrated into HITRAN2016. Spectra from high-resolution laboratory observations, predominantly from Fourier transform spectrometers, are now provided for 328 compounds in the IR spectral range. Spectra for atmospherically-important compounds organized by chemical category are presented. The HITRAN infrastructure (www.hitran.org), HITRAN Application Programming Interface (HAPI), and best practices for searching and downloading data are discussed.

N2 and H2 broadened isobutane infrared absorption cross sections and butane upper limits on Titan

High resolution infrared absorption cross sections of isobutane, (CH3)3CH, were measured in the 1050–1900 cm−1 spectral range by Fourier transform spectroscopy. Four sample temperatures (210, 234, 265 and 296 K) were used with three pressures (10, 30 and 100 Torr) of N2 and H2 broadening gas. Spectra of pure isobutane samples were also recorded. These cross sections are useful for the interpretation of infrared spectra of the Giant Planets and Titan. The isobutane cross sections give an upper limit of 3.91e-8 for its fractional abundance on Titan based on CIRS/Cassini infrared spectra. Using n-butane, CH3(CH2)2CH3, cross sections from the literature, we obtain an upper limit of 5.13e-7 for its abundance on Titan. The combined upper limit for both isomers of butane, C4H10, on Titan of 5.52e-7 is consistent with the lower limit of recent model predictions.

Surface-enhanced infrared absorption

Infrared spectroscopy is a powerful tool for the detection and identification of molecules. However, its application is limited by the low infrared absorption cross-sections of molecules. Localized surface plasmon resonances in metal and highly-doped semiconductor nanomaterials can produce large localized electromagnetic field enhancements. When molecular vibrations are in resonance with localized surface plasmon resonances, molecular vibrations are able to be largely amplified. The detection of minute amounts of target molecules can be realized in this way. Surface-enhanced infrared absorption (SEIRA) spectroscopy has recently attracted extensive attention owing to its enormous potential in molecular detection in chemistry, biology and medicine. In this review article, the enhancement mechanism and theoretical models of SEIRA are first introduced. The preparation methods and enhancement effects of various infrared-responsive nanomaterials are then discussed. The applications of SEIRA in diverse areas, such as hyperspectral infrared chemical imaging, detection of biomolecules, monitoring of pollutants in the environment, and on-chip gas sensing, are finally summarized.

He and H2 broadened propane cross sections in the 3 µm region at cold temperatures

Infrared absorption cross sections of pure propane, as well as propane broadened by He or H2, have been obtained from spectra recorded using Fourier transform instruments located at the Old Dominion University (ODU) and at the Canadian Light Source (CLS). Pressure and temperature regimes for He and H2 foreign gas broadening range from 10 Torr to 300 Torr between 298 K and 200 K. The integrated absorption cross sections were compared to reference data obtained from the Pacific Northwest National Laboratory (PNNL) spectroscopic database, with most values lying within ±10% of their expected values.

Infrared absorption cross sections for air-broadened 1,1-dichloro-1-fluoroethane (HCFC-141b)

1,1-dichloro-1-fluoroethane (CC12FCH3; HCFC-141b), a hydrochlorofluorocarbon (HCFC) used as a foam blowing agent, a solvent in electronics, and for precision cleaning applications, is currently being phased out under the terms of the Montreal Protocol because it depletes stratospheric ozone. In order to monitor its concentration profiles using infrared-sounding instruments, for example the Atmospheric Chemistry Experiment – Fourier transform spectrometer (ACE-FTS), accurate laboratory spectroscopic data are required. This work describes new high-resolution infrared absorption cross sections of 1,1-dichloro-1-fluoroethane / dry synthetic air over the spectral range 705–1280 cm−1, derived from spectra recorded using a high-resolution Fourier transform spectrometer (Bruker IFS 125HR) and a 26 cm-pathlength cell. Spectra were recorded at resolutions between 0.01 and 0.03 cm−1 (calculated as 0.9/MOPD; MOPD = maximum optical path difference) over a range of temperatures and pressures (7.5–760 Torr and 188–295 K). This new cross-section dataset is the first for air-broadened HCFC-141b over a range of pressures and temperatures appropriate for atmospheric conditions.

Infrared absorption cross-sections in HITRAN2016 and beyond: Expansion for climate, environment, and atmospheric applications

Spectroscopic analysis of hydrocarbons, halocarbons and related species is required in atmospheric applications such as climate-change research, tracking of pollution and biomass burning, and remote sensing. Critically evaluated line-by-line spectroscopic data are needed for such analyses. To address this need we report the large addition of spectra to the HITRAN2016 database. This extension increases the number of molecules in the database by almost a factor of 6 from that in HITRAN2012. Spectra from the Pacific Northwest National Laboratory database (Appl. Spectrosc. 2004;58:1452–61) and the Hodnebrog et al. compilation (Rev Geophys 2013;51:300–78) have been integrated into HITRAN2016. Spectra from high-resolution laboratory observations, predominantly from Fourier transform spectrometers, are now provided for 328 compounds in the IR spectral range. Spectra for atmospherically-important compounds organized by chemical category are presented. The HITRAN infrastructure (www.hitran.org), HITRAN Application Programming Interface (HAPI), and best practices for searching and downloading data are discussed.

Infrared absorption cross sections of isobutane with hydrogen and nitrogen as broadening gases

Infrared absorption spectra of isobutane (C4H10) were recorded in the CH stretching spectral region (2500–3280 cm−1) by high resolution Fourier transform spectroscopy (Bruker IFS 125 HR). These spectra were taken at temperatures and pressures appropriate for the gas giant planets Jupiter and Saturn, as well as for Saturn's moon Titan. Absorption cross sections were obtained for pure samples and with broadening gases relevant in those atmospheres, hydrogen and nitrogen, to further simulate the astronomical environments. Corrections to the cross sections were made using data from the Pacific Northwest National Laboratory (PNNL) infrared database.

Metasurface based on cross-shaped plasmonic nanoantennas as chemical sensor for surface-enhanced infrared absorption spectroscopy

Infrared spectroscopy is an effective technique extensively used in research and industry for the label-free and unambiguous identification of molecular species. However, the sensitivity of this technique is severely limited as a result of Beer’s law and, the small infrared absorption cross-section that make prohibitively weak the absorption signals, of minute amounts of analyte as those present in monolayers. This limitation can be overcome by enhancing the infrared vibration of molecules through the enhancement of the electromagnetic (EM) field. Surface Enhanced InfraRed Absorption (SEIRA) using resonant metal Nano-scale Antennas (NAs) can provide huge electromagnetic fields on the nanometer scale featuring localized collective oscillations of electrons, an effect named Localized Surface Plasmonic Resonances (LSPRsWe here report on a series of 2D arrays of cross-shaped NAs having several mm2 area coverage (metasurface) as SEIRA optimized antennas, which can be used in practical applications such as the vibrational sensing of chemical and biological analytes. Cross-shape designed NAs are insensitive to the polarization of the electromagnetic radiation impinging the active area. Due to the random orientation of the dipole moments of molecules they are particularly suitable for the construction of bio-molecular sensors. At the same time, the 2D-array configuration ensures a good near-field signal enhancement arising from the coupling between neighbour NAs Moreover, SEIRA NAs can be easily integrated with micrometre-sized channels and be suitable for the high sensitivity, real time analysis of IR emitting samples, in matrices where IR spectroscopy is severely limited due to absorption bands of liquid water. We present the design, fabrication and experimental characterization of large-area metasurfaces based on cross-shaped plasmonic NAs for the spectroscopic characterization of various types of compounds and for sensing applications in the mid-infrared range. The cross-shaped NAs we have designed exhibit SEIRA phenomena which are very sensitive to both refractive index changes in the surrounding medium and to the specific molecular vibration band emerging from surface adsorbed molecules. To test this effect on our device, we have used as model compounds small molecules (molecular weight (MW) < 500 g/mol) containing triple bond groups resonating at about 2100 cm−1 and a large polymer (MW ˜ 950,000 g/mol) containing carbonyl groups resonating at wavenumbers of about 1700 cm−1. We show a sensitivity of 600 nm/RIU at different wavelengths at a maximum amount of immobilized small molecule of 0.7 fmoles and a SEIRA enhancement factor of 48,000. We also show the device potential to reveal chemical reactions, occurring on the sensor surface at the same scale, where the nitrile group is converted to a triazole ring.

Infrared absorption cross sections of several organo-phosphorous chemical-weapon simulants

Due to extreme toxicity of chemical warfare agents, experiments to study their combustion behavior are commonly carried out using Organo Phosphorous Compounds (OPCs) as simulants. In this study, gas phase absorption cross sections of five common OPC simulants - TMP, DMMP, TEP, DEMP and DIMP have been measured within 650–3500 cm−1 wavenumber range (2.85–13.33 µm) at 295 K and 1 atm pressure (broadening gas: N2). The quantitative absorption spectra reported in this study will be useful in setting up laser based diagnostics schemes to study their chemical kinetics in a shock tube.

New and improved infrared absorption cross sections for trichlorofluoromethane (CFC-11)

Abstract. Trichlorofluoromethane (CFC-11), a widely used refrigerant throughout much of the twentieth century and a very potent (stratospheric) ozone-depleting substance (ODS), is now banned under the Montreal Protocol. With a long atmospheric lifetime, it will only slowly degrade in the atmosphere, so monitoring its vertical concentration profile using infrared-sounding instruments, and thereby validating stratospheric loss rates in atmospheric models, is of great importance; this in turn requires high-quality laboratory spectroscopic data. This work describes new high-resolution infrared absorption cross sections of trichlorofluoromethane/dry synthetic air over the spectral range 710–1290 cm−1, determined from spectra recorded using a high-resolution Fourier transform spectrometer (Bruker IFS 125HR) and a 26 cm pathlength cell. Spectra were recorded at resolutions between 0.01 and 0.03 cm−1 (calculated as 0.9/MOPD; MOPD: maximum optical path difference) over a range of temperatures and pressures (7.5–760 Torr and 192–293 K) appropriate for atmospheric conditions. This new cross-section dataset improves upon the one currently available in the HITRAN (HIgh-resolution TRANsmission) and GEISA (Gestion et Étude des Informations Spectroscopiques Atmosphériques) databases through an extension to the range of pressures and temperatures, improved signal-to-noise and wavenumber calibrations, the lack of channel fringing, the better consistency in integrated band intensities, and additionally the coverage of the weak combination band ν2+ν5.

ExoMol line lists – XXIX. The rotation-vibration spectrum of methyl chloride up to 1200 K

Comprehensive rotation-vibration line lists are presented for the two main isotopologues of methyl chloride, 12CH335Cl and 12CH337Cl. The line lists, OYT-35 and OYT-37, are suitable for temperatures up to |$T=1200\,$| K and consider transitions with rotational excitation up to J = 85 in the wavenumber range 0 – |$6400\,$| cm−1 (wavelengths |$\lambda \gt 1.56\,\mu$|m). Over 166 billion transitions among 10.2 million energy levels have been calculated variationally for each line list using a new empirically refined potential energy surface, determined by refining to 739 experimentally derived energy levels up to J = 5, and an established ab initio dipole moment surface. The OYT line lists show excellent agreement with newly measured high-temperature infrared absorption cross-sections, reproducing both strong and weak intensity features across the spectrum. The line lists are available from the ExoMol database and the cds database.

Semiempirical Atom-centered Density Matrix Propagation Approach to Temperature-dependent Vibrational Spectroscopy of Irinotecan

In the present study, a molecular dynamics study of irinotecan molecule with the atom-centered density matrix propagation scheme was carried out at AM1 semiempirical level of theory, at series of different temperatures, ranging from 5 K to 300 K. Molecular dynamics simulations were performed within the NVE ensemble, initially injecting (and redistributing among the nuclei) various amounts of nuclear kinetic energies to achieve the desired target temperatures. Subsequently to initial equilibration phase of 2 ps, productive simulations were carried out for 8 ps. The accuracy of simulations and the closeness of the generated trajectory to those at the Born-Oppenheimer surface were carefully followed and analyzed. To compute the temperature-dependent rovibrational density of states spectra, the velocity-velocity autocorrelation functions were computed and Fourier-transformed. Fourier-transformed dipole moment autocorrelation functions were, on the other hand, used to calculate the temperature-dependent infrared absorption cross section spectra. The finite-temperature spectra were compared to those computed by a static approach, i.e. by diagonalization of mass-weighted Hessian matrices at the minima located on the potential energy surfaces. Thermally-induced spectral changes were analyzed and discussed. The advantages of finite-temperature statistical physics simulations based on semiempirical Hamiltonian over the static semiempirical ones in the case of complex, physiologically active molecular systems relevant to intermolecular interactions between drugs and drug carriers were pointed out and discussed.

Investigating the evolution of local structure around Er and Yb in ZnO:Er and ZnO:Er, Yb on annealing using X-ray absorption spectroscopy

The local structure around Er and Yb centre in ZnO favouring upconversion luminescence was studied using EXAFS (Extended X-ray absorption fine structure spectroscopy). Due to the ionic radii difference between Zn and Er, Yb ions, the dopants cannot replace Zn in the ZnO lattice properly. Er2O3 and Yb2O3 impurity phases are formed at the grain boundaries of ZnO. It is found that the local structure around the Er centre in ZnO is modified on annealing in air. The symmetry around both erbium and ytterbium reduces with increase in annealing temperature. Symmetry reduction will favour the intra-4f transition and the energy transitions causing upconversion luminescence. By fitting the EXAFS data with theoretically simulated data, it is found that the Er centre forms a local structure similar to C4ν symmetry which is a distorted octahedron. On annealing the sample to 1200 °C, all the erbium centres are transformed to C4ν symmetry causing enhanced upconversion emission. Yb centre has also been modified on annealing. The decrease in co-ordination number with annealing temperature will decrease the symmetry and increase the near infrared absorption cross section. The decrease in symmetry around both the erbium and ytterbium centre and formation of C4ν symmetry around Er centre is the reason behind the activation of upconversion luminescence with high temperature annealing in both Er doped and Er, Yb co-doped ZnO samples. The study will be useful for the synthesis of high efficiency upconversion materials.

High temperature infrared absorption cross sections of methane near 3.4 µm in Ar and CO2 mixtures

The absorption cross-sections of CH4 at two wavelengths in the mid-IR region: λpeak = 3403.4 nm and λvalley = 3403.7 nm were measured. Data were taken using three different compositions of non-reactive gas mixtures comprising CH4/Ar/CO2 between 700 < T < 2000 K and 0.1 < P < 1.5 atm in a shock tube utilizing a continuous-wave distributed-feedback quantum cascade laser. Also, broadband room temperature methane cross section measurements were performed using a Fourier transform infrared spectrometer and the cascade laser to gain a better insight into the changes of the line shapes in various bath gasses (Ar, CO2, and N2). An application of the high-temperature cross-section data was demonstrated to determine the concentration of methane during oxy-methane combustion in a mixture of CO2, O2, and Ar. Current measurements will be valuable addition to the spectroscopy database for methane- an important fuel used for power generation and heating around the world.

Reaction kinetics of (CF3)2CFCN with OH radicals as a function of temperature (278–358 K): A good replacement for greenhouse SF6?

In many industrial applications, (CF3)2CFCN has been suggested as SF6 substitute, which possess a global warming potential (GWP100-yr) of 23500 relative to CO2. The temperature dependence of the rate coefficient (kOH) for the OH+(CF3)2CFCN reaction is reported for the first time: kOH(278–358K)=(5.9±3.2)×10−13exp{−(1856±162)/T}cm3 molecule−1s−1. A lifetime of 47years was estimated relative to that of CH3CCl3. Infrared absorption cross sections were also determined to derive the radiative efficiency (0.28Wm−2ppbv−1). A GWP100-yr of 3646 was estimated, resulting in a significant reduction of the contribution to global warming if SF6 was replaced by (CF3)2CFCN.

The HITRAN2016 molecular spectroscopic database

This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.

Helium broadened propane absorption cross sections in the far-IR

Infrared absorption spectra for pure and He broadened propane have been recorded in the far-IR region (650-1300cm−1) at the Canadian Light Source (CLS) facility using either the synchrotron or internal glowbar source depending on the required resolution. The measurements were made for 4 temperatures in the range 202–292K and for 3 pressures of He broadening gas up to 100Torr. Infrared absorption cross sections are derived from the spectra and the integrated cross sections are within 10% of the corresponding values from the Pacific Northwest National Laboratory (PNNL) for all temperatures and pressures.