Fourier Transform Absorption Spectra Research Articles

The ammonia absorption spectrum between 3900 and 6350 cm-1: 15NH3 contribution and a recommended list for natural ammonia

Following previous contributions dedicated to the main isotopologue, 14NH3, in the present work, we examine the 15NH3 absorption spectrum between 3950 and 6350 cm-1 in order to elaborate an absorption line list for ammonia in natural isotopic abundance. For this purpose, several room temperature Fourier Transform absorption spectra of ammonia highly enriched in 15NH3 measured in the 90′s and available from the Kitt Peak data centre have been analysed. In addition, a more recent high-resolution spectrum recorded in Brussels between 4150 and 4600 cm-1 is also considered. The spectra were divided in three separate intervals (3900–4706, 4706–5650 and 5650–6350 cm-1) for which experimental lists including 3506, 3788, and 2317 lines, respectively, were retrieved and treated independently. By comparison with an ab initio line list (the BYTe list) and systematically validating the assignments by using lower state combination difference relations (LSCD), 2013, 1771 and 570 transitions could be assigned in the three regions, respectively. They belong to 16, 22, and 10 bands and correspond to 98.5, 92.6 and 78.6 % of the experimental intensities in the region, respectively. For comparison, only four 15NH3 bands were previously assigned in the literature in the entire studied region.The obtained 15NH3 assigned line lists were gathered with the previously elaborated line list of the main isotopologue to produce a recommended line list for natural ammonia between 3900 and 6350 cm-1.

Absorption of methane broadened by carbon dioxide in the 3.3 μm spectral region: From line centers to the far wings

This work studied the infrared absorption of methane broadened by carbon dioxide, which can contribute to the radiative budget of CO2-dominated atmospheres. Fourier transform absorption spectra of CH4 perturbed by CO2 were recorded in the 3.3 μm spectral region, at room temperature and total pressures ranging from 3 to 25 bars. These experimental data were modeled using a theoretical approach taking collision-induced line mixing into account. Comparisons between measured and calculated spectra demonstrate that the proposed model is capable of accurately representing the absorption of methane broadened by collisions with CO2, from line centers to the far wings. For practical applications, this rigorous spectral modeling was used to derive a simple χ-factor model to represent the spectral shape of CO2-broadened CH4 line wings. Comparisons with experimental values show that, at room temperature, the proposed χ-factor reproduces the measured spectra to within 10% in the band wings where the absorption is mainly due to the far line wings, while the usual Lorentzian profile leads to relative differences several orders of magnitude larger. This line-shape correction was successfully validated through comparisons with heavily saturated spectra of the ν3 band of methane recorded at sub-atmospheric pressures.

Te2 absorption spectrum from 19000 to 24000 cm−1

A Fourier-transform absorption spectrum of 130Te2 has been recorded from 19000 to 24000 cm−1 at approximately 620 °C; a transmission spectrum is made available in ASCII format. The spectrum is intended to aid spectral calibration in the blue-violet region. It extends slightly beyond the paper version of the Tellurium atlas, published in 1980 (J. Cariou and P. Luc, 'Atlas du spectre d'absorption de la molécule de tellure', Laboratoire Aime-Cotton (1980)).

Visible Fourier transform absorption spectrum measurement method based on dual interferometer configuration

We introduce an absorption spectrum measurement method in the visible regime based on dual interferometer configuration. The proposed method can realize the measurement of the absorption spectrum by addition and calculation of the alternating current (AC) components of interferograms from dual symmetrical interferometers in one measurement, with no need to subtract twice-measured spectrum data with or without samples in the traditional single interferometer method, thus expanding the dynamic range of measurement, especially suitable for weak absorption. The absorption spectra of FB570-10 bandpass filter and NF533-17 notch filter measured by this method conform to the official data.

The absorption spectrum of ammonia between 5650 and 6350 cm−1

A room temperature Fourier Transform absorption spectrum of ammonia measured in 1991 and available from the Kitt Peak data center is analyzed in the 5650 - 6350 cm−1 region. This spectral interval is part of the important 1.6 µm atmospheric transparency window where ammonia could be detected as trace species. The centers and intensities of 2779 ammonia lines were retrieved using a multiline fitting procedure. The spectrum was assigned by the joint use of a recent variational line list and of lower state combination difference relations. Overall, 1762 lines were assigned to 29 bands providing 914 new experimental energies. The obtained assignments and upper state experimental energies are the first for ammonia in the studied region. The comparison of our line list to the variational line list, to the HITRAN2016 list and to a very recent experimental line list is presented and discussed.

Possible cause of chemiluminescence in silicone rubber

Chemiluminescence (CL) was observed in silicone rubber (SiR), an important electrical insulating material. Fourier-transform mid-infrared absorption spectra were also measured before and after the CL measurement. When SiR was heated at 250 °C, CL clearly appeared in 20 min. It was also confirmed that no carbonyl groups were induced by the heating during the CL measurement. A possible mechanism to explain these results is that the oxidation of silicon, which induces the cross-linking of siloxane bonds and the formation of silica particles, generates the CL.

FTIR spectrum of hydrogen sulfide between 9995 and 10,310 cm−1

Fourier transform absorption spectrum of H2S molecule in the 9995–10,310 cm−1 spectral region from [Bykov A, Naumenko O, Smirnov M, Sinitsa L, Brown L, Crisp J, Crisp D. Can. J. Phys 1994; 72:989] has been theoretically assigned and modeled in the frame of the effective Hamiltonian approach. A set of 205 experimental energy levels has been derived for the (004) and (103) vibrational states at 10,188.303 and 10,194.445 cm−1, respectively. These levels have been reproduced with the root mean square deviation of 0.004 cm−1 by the fitting of 28 parameters of the Watson-type rotational Hamiltonian, as well as resonance parameters accounting for the Coriolis- and Fermi- type resonance interactions between (004) and (103) “bright” states, and (400) “dark” state at 10,292.536 cm−1. Detailed comparison of the experimental line position and intensities with recent variational calculations is presented.

Fourier Transform Spectroscopy of two trace gases namely Methane and Carbon monoxide for planetary and atmospheric research application

Two atmospheric trace gases, namely methane and carbon monoxide have been considered in this study. Fourier transform absorption spectra of the 2–0 band of 12C16O mixed with CO2 have been recorded at total pressures from 156 to 1212 hPa and at 4 different temperatures between 240 K and 283 K. CO2 pressure-induced line broadening and line shift coefficients, and the associated temperature dependence have been measured in an multi-spectrum non-linear least squares analysis using Voigt profiles with an asymmetric profile due to line mixing. The measured CO2-broadening and CO2-shift parameters were compared with theoretical values, calculated by collaborators. In addition, the CO2-broadening and shift coefficients have been calculated for individual temperatures using the Exponential Power Gap (EPG) semi-empirical method. We also discuss the retrieved line shape parameters for Methane transitions in the spectral range known as the Methane Octad. We used high resolution spectra of pure methane and of dilute mixtures of methane in dry air, recorded with high signal to noise ratio at temperatures between 148 K and room temperature using the Bruker IFS 125 HR Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory, Pasadena, California. Theoretical calculations for line parameters have been performed and the results are compared with the previously published values and with the line parameters available in the GEISA2015 [1] and HITRAN2012 [2] databases.

A near infrared line list for NH3: Analysis of a Kitt Peak spectrum after 35 years

A Fourier Transform (FT) absorption spectrum of room temperature NH3 in the region 7400–8640cm−1 is analysed using a variational line list and ground state energies determined using the MARVEL procedure. The spectrum was measured by Dr. Catherine de Bergh in 1980 and is available from the Kitt Peak data center. The centers and intensities of 8468 ammonia lines were retrieved using a multiline fitting procedure. 2474 lines are assigned to 21 bands providing 1692 experimental energies in the range 7500–9200cm−1. The spectrum was assigned by the joint use of the BYTe variational line list and combination differences. The assignments and experimental energies presented in this work are the first for ammonia in the region 7400–8640cm−1, considerably extending the range of known vibrational-excited states.

CO2 pressure broadening and shift coefficients for the 2–0 band of 12C16O

Fourier transform absorption spectra of the 2–0 band of 12C16O mixed with CO2 have been recorded at total pressures from 156 to 1212hPa and at 4 different temperatures between 240K and 283K. CO2 pressure-induced line broadening and line shift coefficients, and the temperature dependence of the former have been measured including line mixing using a multi-spectrum non-linear least squares fitting technique. Different line shape models have been considered to take into account the Dicke narrowing or speed dependence effects. Measured line-shape parameters were compared with theoretical values, calculated for individual temperatures using a semi-empirical method and the Exponential Power Gap (EPG) law.

The Fourier transform absorption spectrum of acetylene between 8280 and 8700 cm−1

High resolution (0.011cm–1) room temperature (295K) Fourier transform absorption spectra (FTS) of acetylene have been analyzed in the 8280–8700cm−1 range dominated by the ν1+ν2+ν3 band at 8512cm−1. Line positions and intensities were retrieved from FTS spectra recorded at 3.84 and 56.6hPa. As a result, a list of 1001 lines was constructed with intensities ranging between about 2×10−26 and 10−22cm/molecule. Comparison with accurate predictions provided by a global effective operator model led to the assignment of 629 12C2H2 lines. In addition, 114 lines of the 13C12CH2 isotopologue were assigned using information available in the literature. The 12C2H2 lines belong to thirteen bands, nine of which being newly reported. The 13C12CH2 lines belong to three bands, the intensities of which being reported for the first time. Spectroscopic parameters of the 12C2H2 upper vibrational levels were derived from band-by-band analyses of the line positions (typical rms are on the order of 0.002cm−1). Three of the analyzed bands were found to be affected by rovibrational perturbations, which are discussed in the frame of a global effective Hamiltonian. The obtained line parameters are compared with those of the two bands included in the HITRAN 2012 database.

The Fourier transform absorption spectrum of acetylene between 7000 and 7500 cm–1

High resolution (0.011cm–1) room temperature (295K) Fourier transform absorption spectra (FTS) of acetylene have been recorded between 7000 and 7500cm–1. Line parameters (positions, intensities and self broadening coefficients) have been measured using a multispectrum treatment of three FTS spectra, recorded at 3.84, 8.04 and 56.6hPa. As a result, a list of 3788 lines was constructed with intensities ranging between about 10–26 and 10–22cm/molecule. Comparison with accurate predictions provided by a global effective operator model (Lyulin OM, Perevalov VI, Teffo JL, Proc. SPIE 2004;5311:134–43) led to the assignment of 2471 of these lines to 12C2H2. The assigned lines belong to 29 12C2H2 bands, 12 of them being newly reported. Spectroscopic parameters of the upper vibrational levels were derived from band-by-band fits of the line positions (typical rms values are on the order of 0.001cm–1). About half of the analyzed bands were found to be affected by rovibrational perturbations. Line parameters obtained in this work were compared with those available for about 350 transitions in the HITRAN 2012 database. The large set of new data will be valuable to refine the parameters of the global effective Hamiltonian and dipole moments of 12C2H2.

Estimation of Aromatic Structure Contents in Hardwood Lignins from IR Absorption Spectra

Results of an in-depth analysis of Fourier-transform IR absorption spectra of hardwood and softwood dioxane lignins were reported. Correlations between absorption band intensities in initial and second-derivative spectra and 13C NMR spectroscopic data on the contents of guaiacyl and syringyl structural units were found. The found linear dependences enabled the contents of two types of phenylpropane units to be estimated in the range 0–100% with a relative error of ≤5%.

Temperature dependence of nitrogen and oxygen-broadening of the 16O3 υ1 band

High-resolution Fourier transform absorption spectra of ozone broadened by N2 and O2 have been recorded at room temperature and at 225 K. Nitrogen and oxygen-broadened half-widths and their temperature dependence have been determined for 40 ro-vibrational transitions of the 16O3 ν1 band near 1103 cm−1 with a wide range of the rotational quantum number J (12–40) have been determined.

Temperature dependence of nitrogen and oxygen broadening of the 16O3 ν 3 band

High-resolution Fourier transform absorption spectra of ozone broadened by N2 and O2 have been recorded at room temperature and at 225 K. Nitrogen- and oxygen-broadened half-widths and their temperature dependence for respectively 160 ro-vibrational transitions on the 16O3 ν 3 band with a wide range of rotational quantum numbers J (2–48) and Ka (0–8) have been determined.

High-resolution infrared spectroscopy of [formula omitted] in the 3500–9000 cm −1 region

The Fourier-transform absorption spectrum of 15 N 2 16 O -enriched nitrous oxide has been recorded at the Doppler limited resolution in the spectral range 3500–9000 cm −1. 6523 Transitions of 15 N 2 16 O were observed and assigned based on the global effective Hamiltonian model. The band-by-band analysis led to the determination of the ro-vibrational parameters of a total of 65 bands. Among these bands, 39 are newly observed, and the rotational analysis of 26 others were significantly extended and improved.

Fourier-transform spectroscopy of 15N14N16O in the 3500–9000cm−1 region

Abstract The Fourier-transform absorption spectrum of 15N14N16O-enriched nitrous oxide has been recorded at the Doppler limited resolution in the spectral range 3500–9000 cm−1. More than 15 000 transitions of 15N14N16O were observed and assigned based on the global effective Hamiltonian model. The band-by-band analysis led to the determination of the ro-vibrational parameters of a total of 133 bands. Among these bands, 103 were newly observed, and the rotational analysis of 30 others were significantly extended and improved.

Critical evaluation of measured rotation–vibration transitions and an experimental dataset of energy levels of HD 18O

All available transitions from microwave to visible region (0.2–12 105 cm −1) of the HD 18O molecule were collected and tested using the RITZ computer code. Literature data were completed by transitions assigned to HD 18O in long path Fourier transform absorption spectra of the H 2O, HDO and D 2O gas mixtures with natural abundance of oxygen-18. In addition about 40 unassigned lines between 4200 and 6600 cm −1 of our previous water study associated with the HD 18O molecule have been found and assigned. The new long path absorption spectra of the HDO and D 2O mixtures allow us to observe about 1000 transitions of HD 18O in the 6125–10 720 cm −1 spectral region. These data have been critically analyzed and used to obtain the most complete and precise set of the experimental energy levels of this molecule.

The local dynamics of polyetherimides: Conformational probes, IR Fourier transform spectra, and quantum-chemical calculations

The IR Fourier transform absorption spectra were used to study the rotational mobility of macromolecule fragments (local dynamics) of several vitreous polyetherimides by the method of conformational probes. The temperatures of the freezing of conformational equilibria of probes were determined. The IR spectra of diphenyl ether, 2,2-diphenylpropane, phthalimide, and N-phthalimide were studied; these molecules were used as models of fragments of monomeric units of polyetherimides. Quantum-chemical calculations of the energies and vibrational spectra of these molecules were performed by the B3LYP method with the 6–31G(d,p) basis set. The rotational mobility of benzene rings in the main chain of polyetherimide macromolecules was estimated, and the nature of secondary relaxation transitions was determined. The IR spectra of polyetherimides were interpreted. The rotational mobility of the CH3 and CF3 groups of polyetherimides was estimated from the temperature dependence of absorption band contours of these groups.

High-resolution spectroscopy of the triple-substituted isotopologue of water molecule D_{\\bf 2}^{\\bf 18}O: the first triad

The high-resolution Fourier-transform absorption spectrum of the triple-substituted isotopologue of the water molecule, DO is measured in the 1700–9000 cm−1 region. The transitions of the ν1, 2ν2 and ν3 bands are assigned with the help of the high accuracy variational calculations based on an empirical mass-dependent Partridge–Schwenke potential energy surface. The fittings based on an effective Hamiltonian model are also utilized to confirm the assignments. A set of 816 precise ro-vibrational energy levels for the first triad of interacting vibrational states: (0 0 1), (1 0 0) and (0 2 0) is retrieved. With the upper state combination differences, the ground state energy levels are extended to J max = 23 and . These levels can be used to check the quality of the recently available high accuracy ab initio potential energy surface of the water molecule.