GEISA Databases Research Articles

New line list for the ν4 bands of the trans (790.117 cm–1) and cis (851.943 cm–1) conformers of nitrous acid (HONO): Accurate positions and absolute intensities

The goal of this work was to update and significantly improve the line lists that have been generated recently for 11 µm bands of the trans- and cis- conformer forms of nitrous acid (HONO) [Armante R, Perrin A, Kwabia Tchana F, Manceron L. The ν4 bands at 11 μm: linelists for the trans- and cis- conformer forms of nitrous acid (HONO) in the 2019 version of the GEISA database. Molecular Physics 2021;120:e1951860]. That 2019 version of the 11 µm line list was generated using the spectroscopic parameters that were available, at that time, in the literature. During the present study, we used high-resolution Fourier transform spectra recorded at 11 µm to perform a large investigation of line positions and intensities for the ν4 bands of the trans- and cis-conformer of HONO. The resulting set of experimental ν4 (absolute) intensities and of 41 energy levels were used to determine, by least squares fit computations, improved position and intensity parameters for the ν4 bands of the trans- and cis-conformer of HONO. For trans-HONO, the ν4 band appeared not to be perturbed, while for cis-HONO a weak high order B-type Coriolis, coupling together the 41 and 61 energy levels was evidenced for the first time. This new list is of potential interest for the IASI-NG (Infrared Atmospheric Sounding Interferometer - New Generation) instrument which will be launched on board the METOP-SG satellite in 2025.

New acetylene line list near 3.8-μm – Part II

The investigation of the 3.8 µm spectral region of acetylene 12C2H2 main isotopologue has been completed from spectra recorded with Fourier Transform Spectrometer (FTS) using high optical path length. This work is the second of a series dedicated to the ΔP = 4 spectral region. In the first paper of the series (JQSRT 2023;295:108413) 14 bands of 12C2H2 were studied in the beginning of the region. In the present work the whole ΔP = 4 spectral region was investigated. 52 newly observed vibrational bands have been studied as well as the 5 intense bands present in the HITRAN and GEISA databases. The band centers and the upper level spectroscopic constants were retrieved for all bands. The comparison with the data from HITRAN and GEISA databases revealed important deviations from the measurements due to wrong extrapolations (especially line positions). The effective dipole moment operator parameters describing intensities of all transitions observed in the ΔP = 4 spectra region were refined. A complete list of calculated line parameters for 7515 transitions has been generated for 71 bands between 2389 cm−1 and 2890 cm−1.

The rotational spectrum of HD broadened by H2 at temperatures between 100 – 296 K

Laboratory measurements of the R(0) – R(3) pure rotational transitions of hydrogen deuteride (HD) have been performed at low pressures (< 1 bar) and temperatures between 98 and 296 K. The measurements were conducted using a Fourier transform spectrometer coupled to the Soleil synchrotron far-infrared source to obtain pure HD and HD-H2 mixture spectra. The observed spectra have been fitted using a non-linear least-squares multispectral fitting program. For each transition the line position, intensity, pressure broadening, pressure-induced frequency shift, and the temperature dependencies of these quantities have been determined simultaneously. These spectroscopic line parameters are compared to previous measurements made at higher gas pressures. Notably the present, and previous, measurements of the self- and H2-broadened linewidths are smaller by a factor of five compared with those listed in the HITRAN and GEISA databases. This work is applicable to the low pressure, low temperature regimes found in the atmospheres of the giant gaseous planets.

The 5.8 µm absorption bands for nitric acid (H14N16O3): line positions and intensities for the ν2 band at 1709.567 cm−1 and for its first associated hot bands (ν2+ν9−ν9, ν2+ν7−ν7, ν2+ν6−ν6)

This paper is the second of two back-to-back works, whose goal was to generate a more accurate linelist for the 5.8 µm absorption band of HNO3. Here, we report improved line positions and intensities in the ν2 cold band which is the main band in this region. For this, we recorded four high-resolution Fourier transform spectra for the ν2 band, centered at 1709.567 cm−1, under different experimental conditions. Using these spectra, a new extended line position analysis was performed for the ν2 band, leading to more accurate line positions. In parallel, individual line intensities were measured. It appears that, although the ν2 band is mainly of B-type, it also possesses a (very) weak A-type component that cannot be ignored. Overall, the line intensities in this new database are about 8% weaker than those quoted presently in the HITRAN (https://hitran.org/) or GEISA (https://geisa.aeris-data.fr/) databases. Our final linelist for HNO3 at 5.8 µm is provided as a supplement to this paper. It includes lines from the ν2 band together with those of the ν2+ν9−ν9, ν2+ν6−ν6, and ν2+ν7−ν7 associated hot bands that were generated during the first part of this study, described in the companion paper.

The ν4 bands at 11 µm: linelists for the Trans- and Cis- conformer forms of nitrous acid (HONO) in the 2019 version of the GEISA database*

Using parameters of line positions and line intensities existing in the literature for the Trans- and Cis- conformer forms of nitrous acid (HONO), we generated, for the first time, a linelist of positions, intensities, and line shape parameters for the ν4 bands of nitrous acid located at 790.117 and 851.943 cm−1 for the Trans- and Cis- conformers, respectively. A validation of this linelist was performed using spectra recorded by the IASI (Interféromètre Atmosphérique de Sondage Infrarouge) satellite instrument in February 2009 during the (rather) exceptional conditions of the large Australian bush fires. This list, which is now included in the 2020 version of the GEISA database (https://geisa.aeris-data.fr/), is of potential interest for the IASI-NG (Infrared Atmospheric Sounding Interferometer – New Generation) instrument which will be launched on board the METOP-SG satellite in 2021.

The 2020 edition of the GEISA spectroscopic database

This paper describes the 2020 release of the GEISA database (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information), developed and maintained at LMD since 1974. GEISA is the reference database for several current or planned Thermal and Short-Wave InfraRed (TIR and SWIR) space missions IASI (Infrared Atmospheric Sounding Interferometer), IASI-NG (IASI New Generation), MicroCarb (Carbon Dioxide Monitoring Mission), Merlin (MEthane Remote sensing LIdar missioN). It is actually a compilation of three databases: the “line parameters database”, the “cross-section sub-database” and the “microphysical and optical properties of atmospheric aerosols sub-database”. The new edition concerns only the line parameters dataset, with significant updates and additions implemented using the best available spectroscopic data.The GEISA-2020 line parameters database involves 58 molecules (145 isotopic species) and contains 6,746,987 entries, in the spectral range from 10−6 to 35877 cm−1. In this version, 23 molecules have been updated (with 10 new isotopic species) and 6 new molecules have been added (HONO, COFCl, CH3F, CH3I, RuO4, H2C3H2 (isomer of C3H4)) corresponding to 15 isotopic species. The compilation can be accessed through the AERIS data and services center for the atmosphere website (https://geisa.aeris-data.fr/), with the development of a powerful graphical tool and convenient searching, filtering, and plotting of data using modern technologies (PostgreSQL database, REST API, VueJS, Plotly).Based on four examples (H2O, O3, O2 and SF6), this paper also shows how the LMD in house validation algorithm SPARTE (Spectroscopic Parameters And Radiative Transfer Evaluation) helps to evaluate, correct, reject or defer the input of new spectroscopic data into GEISA and this, thanks to iterations with researchers from different communities (spectroscopy, radiative transfer).

Validation of spectroscopic data in the 1.27 µm spectral region by comparisons with ground-based atmospheric measurements

Various spectroscopic data for absorption lines due to the magnetic dipole transitions of the a1Δg−X3Σg−(0−0) band of O2 centered at 1.27 µm are tested by comparison with high-resolution ground-based atmospheric measurements recorded by Fourier Transform Spectrometers at Park Falls and Caltech (USA). This band is of importance for atmospheric remote sensing since it will be used (together with the O2 A-band near 760 nm) by the passive short wave infrared spectrometer onboard the MicroCarb satellite mission (i.e. this band includes the B4 band of MicroCarb, from about 7800 cm−1 to 7912 cm−1) for the determination of surface pressure and atmospheric aerosols. Spectroscopic data of the HITRAN2016 and GEISA2015 databases as well as those from recent laboratory studies are here used in a radiative transfer code to simulate atmospheric transmissions under the conditions of the measurements. Comparisons are made for different solar zenith angles and for the whole B4 spectral range considered by MicroCarb. Spectroscopic data of water vapor are also tested by considering both relatively dry and humid atmospheric conditions. Averaging the “calculated-observed” residuals over numerous recordings made for close values of the solar zenith angle and humidity enables reduction of the uncertainties due to the radiometric noise of the instrument and to the imperfect description of the atmospheric state. This enables the detection of systematic differences in the spectral residuals caused by small changes in spectroscopic data. The results show that the spectroscopic parameters in the HITRAN2016 and GEISA2015 databases lead to large residuals while data of two recent laboratory studies, obtained from spectra measured with the cavity ring-down spectroscopy technique using the speed-dependent Nelkin-Ghatak profile lead to much better agreement with atmospheric measurements. Significant residuals are noted for water vapor absorption lines simulated using parameters provided by both the HITRAN and GEISA databases.

The new nitrogen dioxide (NO2) linelist in the GEISA database and first identification of the ν1+2ν3-ν3 band of 14N16O2

We have generated new lists of line position, line intensity and line shape parameters of nitrogen dioxide (14N16O2 and 15N16O2), here labeled as “GEISA-19”, which have been included in the (Gestion et Etude des Informations Spectroscopiques Atmosphériques) GEISA database (https://geisa.aeris-data.fr/). Except for the far infrared and the 13.3 µm regions, all spectral regions of the 1153–4775 cm−1 spectral domain are significantly modified by this major update of the GEISA linelist. For the 6.2 µm and 3.4 µm spectral regions, which correspond to the strongest absorption of NO2, we proceed to a complete replacement of the lists for the first hot bands, ν2 + ν3-ν2 and ν1 +ν2 + ν3-ν2, respectively, and to the inclusion, whenever possible, of higher order hot bands involving the (1,0,0), (0,2,0) and (0,0,1), (1,1,0), (2,0,0) or (0,0,2) states as lower states. Also, the ν1 + ν3 linelist was improved for high rotational quantum numbers and the ν3 and ν1+ν3 bands for 15N16O2, which is the second most abundant isotopologue of NO2, are now included in the database. Finally several weak cold bands in the 2.2–4.9 µm region were added for the first time to the GEISA linelist. These new vibration rotation transitions were generated using existing literature data or making use of experimental data extracted from high resolution Fourier transform spectra recorded at SOLEIL for the purpose of this study. One outcome of this study was the first identification of the ν1+2ν3-ν3 hot band, leading to the first determination of the (1,0,2) energy level parameters. Also, an improved set of parameters was derived for the (0,1,1) state. The validation of the GEISA-19 linelist was performed through a detailed comparison at 296 K between computed and observed Fourier transform laboratory spectra. Also, the consistency, from one band to another, of the energy levels values was carefully checked. Finally inter-comparisons and verifications were performed using the recent versions of the HITRAN (https://hitran.org/) and HITEMP databases [R.J. Hargreaves, I. E. Gordon, L. S. Rothman, S. A. Tashkun, V. I. Perevalov, A. A. Lukashevskaya, S. N. Yurchenko, J. Tennyson, and H. S.P. Müller. J. Quant. Spectrosc. Radiat. Transf. 232 35 (2019)]. Our conclusions are that, at 296 K, GEISA-19 is of better quality than HITRAN2016-updated or HITEMP in the overall 1153–4775 cm−1 spectral region. As compared to its previous version, this new linelist will lead to an improved quality of the NO2 retrievals that will be performed for the future IASI-NG (Infrared Atmospheric Sounding Interferometer New Generation) satellite instrument (https://iasi-ng.cnes.fr/fr). However, contrary to HITEMP, GEISA-19 which does not include transitions involving high rotational quantum numbers or belonging to very high order hot bands cannot be used for hot temperature conditions.

Vibrational dependence, temperature dependence, and prediction of line shape parameters for the H2O-N2 collision system

In a recent work [JQSRT 228,79(2019)], Vispoel et al. optimized the intermolecular potential used in the Modified Complex Robert-Bonamy (MCRB) formalism for the H2O-N2 collision system. Calculations were made for a number of transitions in the rotation and ν2 bands. The needs of the spectroscopic and astrophysics communities include data for water vapor transitions that have multiple vibrational quanta exchanged. In this work, MCRB calculations were made for 0–4 vibrational quanta exchanged in the ν1, ν2, and ν3 bands for 13 temperatures from 200–3000 K; 7272 transitions for each band. From these data, the vibrational and temperature dependence of the half-width and line shift were determined. The temperature dependence was determined using the Gamache-Vispoel model [JQSRT 217, 440(2018)]. The data allowed the development of a routine that can predict the half-width, line shift, and their temperature dependence for transitions not yet studied. The prediction algorithm is based on theory [JQSRT, 83, 119(2004)] and yields line shape parameters with much smaller uncertainty than obtained by fitting with ad hoc polynomials or J” averaged values. A line file based on the 2020 update to the HITRAN2016 water vapor line file was created with N2 as the broadening species. These data are useful for combustion studies and as a first step to determining air-broadening for the HITRAN and GEISA databases.

New line positions analysis of the 2ν 1 and ν 1 + ν 3 bands of NO2 at 3637.848 and 2906.070 cm−1

Using a high-resolution Fourier transform spectrum recorded at SOLEIL for a rather large value of the (pressure × path length) product a new investigation of the very weak 2ν 1 absorption band of nitrogen dioxide, located at 2627.377 cm−1 was performed, together with an extension up to higher N and Ka values of a previous investigation of the strong ν 1 + ν 3 band [J.-Y. Mandin, V. Dana, A. Perrin, J.-M. Flaud, C. Camy-Peyret, L. Régalia and A. Barbe, J. Mol. Spectrosc. 181, 379 (1997)]. The 2ν 1 lines proved to be perturbed by local vibration–rotation resonances which couple the (2,0,0) energy levels with those of the (1,2,0) and (1,0,1) states. Also the (1,0,1) energy levels are also coupled by a C-type Coriolis resonance with those of the (1,2,0) and (2,0,0) energy levels. The final energy levels calculation involves six interacting states of NO2, {(2,0,0), (1,2,0), (1,0,1), (0,0,2), (0,4,0), (0,0,2)}. An estimation of line intensities parameters was performed for the very weak 2ν 1 band. Finally a list of line parameters (positions, intensities and shapes) for the 2ν 1, ν 1 + 2ν 2 and ν 1 + ν 3 bands of NO2, was generated and is now included in the GEISA database (https://geisa.aeris-data.fr/).

Ground-based infrared mapping of H2O2 on Mars near opposition

We pursued our ground-based seasonal monitoring of hydrogen peroxide on Mars using thermal imaging spectroscopy, with two observations of the planet near opposition, in May 2016 (solar longitude Ls = 148.5°, diameter = 17 arcsec) and July 2018 (Ls = 209°, diameter = 23 arcsec). Data were recorded in the 1232–1242 cm−1 range (8.1 μm) with the Texas Echelon Cross Echelle Spectrograph (TEXES) mounted at the 3 m Infrared Telescope Facility (IRTF) at the Mauna Kea Observatories. As in the case of our previous analyses, maps of H2O2 were obtained using line depth ratios of weak transitions of H2O2 divided by a weak CO2 line. The H2O2 map of April 2016 shows a strong dichotomy between the northern and southern hemispheres, with a mean volume mixing ratio of 45 ppbv on the north side and less than 10 ppbv on the south side; this dichotomy was expected by the photochemical models developed in the LMD Mars Global Climate Model (LMD-MGCM) and with the recently developed Global Environmental Multiscale (GEM) model. The second measurement (July 2018) was taken in the middle of the MY 34 global dust storm. H2O2 was not detected with a disk-integrated 2σ upper limit of 10 ppbv, while both the LMD-MGCM and the LEM models predicted a value above 20 ppbv (also observed by TEXES in 2003) in the absence of dust storm. This depletion is probably the result of the high dust content in the atmosphere at the time of our observations, which led to a decrease in the water vapor column density, as observed by the PFS during the global dust storm. GCM simulations using the GEM model show that the H2O depletion leads to a drop in H2O2, due to the lack of HO2 radicals. Our result brings a new constraint on the photochemistry of H2O2 in the presence of a high dust content. In parallel, we reprocessed the whole TEXES dataset of H2O2 measurements using the latest version of the GEISA database (GEISA 2015). We recently found that there is a significant difference in the H2O2 line strengths between the 2003 and 2015 versions of GEISA. Therefore, all H2O2 volume mixing ratios up to 2014 from TEXES measurements must be reduced by a factor of 1.75. As a consequence, in four cases (Ls around 80°, 100°, 150°, and 209°) the H2O2 abundances show contradictory values between different Martian years. At Ls = 209° the cause seems to be the increased dust content associated with the global dust storm. The inter-annual variability in the three other cases remains unexplained at this time.

Measurement of middle infrared spectroscopic parameters of carbon disulfide based on tunable diode laser absorption spectroscopy

Carbon disulfide (CS&lt;sub&gt;2&lt;/sub&gt;) is a toxic volatile sulfur compound with flammability and harmfulness, which can seriously harm the human health and threaten the industrial production safety. Therefore, it is of high importance for monitoring CS&lt;sub&gt;2&lt;/sub&gt; concentration in the air. Tunable diode laser absorption spectroscopy is very suitable for the detection of trace gas for it possesses high sensitivity and fast response. And the precise knowledge of spectroscopic parameters is essential for deducing the CS&lt;sub&gt;2&lt;/sub&gt; concentration. However, primary database including HITRAN and GEISA lacks spectroscopic parameters of CS&lt;sub&gt;2&lt;/sub&gt;. Thus, to address this issue, a measurement system of absorption spectrum is built for determining spectroscopic parameters by using a quantum cascade laser with narrow linewidth and high output power operating near 4.6 um as a light source. In this paper, direct absorption spectroscopy is used to measure the CS&lt;sub&gt;2&lt;/sub&gt; absorption spectra under different sample pressures and the environment temperature is controlled at 296 K, which is adjusted by an air conditioner. We intensively study the absorption spectra of CS&lt;sub&gt;2&lt;/sub&gt; in a range between 2178.99 and 2180.79 cm&lt;sup&gt;–1&lt;/sup&gt;.According to the relevant reports and the need of actual measurement, four absorption lines are mainly measured in a range of 2180.5−2180.74 cm&lt;sup&gt;–1&lt;/sup&gt;. Combining with the multiple linear regression algorithm based on the nonlinear least-square method and Beer-Lambert law, the integrated area and Lorentz line width of measured CS&lt;sub&gt;2&lt;/sub&gt; absorption spectrum can be determined. Then the spectroscopic parameters including absorption line intensity and air broadening coefficient are precisely obtained by linearly fitting the integrated areas and Lorentz line widths of CS&lt;sub&gt;2&lt;/sub&gt; absorption spectra at different pressures. Moreover, nitrous oxide (N&lt;sub&gt;2&lt;/sub&gt;O) absorption spectrum with high spectral resolution is measured to calibrate the central position of carbon disulfide absorption line according to its known line position extracted from HITRAN database and the results obtained by etalon. The calculated results show that the uncertainty of line intensity and air broadening coefficient are less than 5% and 15%, respectively. It demonstrates that the measured spectroscopic parameters of four absorption lines for this study can be recorded in the database of HITRAN, which is very important for trace gas sensing of CS&lt;sub&gt;2&lt;/sub&gt;. In the future, we will further improve the system for measuring CS&lt;sub&gt;2&lt;/sub&gt; absorption line parameters to fill in the gaps in their spectral parameters in HITRAN and GEISA databases.

High-resolution spectroscopy and global analysis of CF4 rovibrational bands to model its atmospheric absorption

CF4, or tetrafluoromethane, is a chemically inert and strongly absorbing greenhouse gas, mainly of anthropogenic origin. In order to monitor and reduce its atmospheric emissions and concentration, it is thus necessary to obtain an accurate model of its infrared absorption. Such models allow opacity calculations for radiative transfer atmospheric models. In the present work, we perform a global analysis (divided into two distinct fitting schemes) of 17 rovibrational bands of CF4. This gives a reliable model of many of its lower rovibrational levels and allows the calculation of the infrared absorption in the strongly absorbing ν3 region (1283 cm−1 / 7.8 μm), including the main hot band, namely ν3+ν2−ν2 as well as ν3+ν1−ν1; we could also extrapolate the ν3+ν4−ν4 absorption. This represents almost 92% of the absorption at room temperature in this spectral region. A new accurate value of the C–F bond length is evaluated to re=1.314860(21)Å. The present results have been used to update the HITRAN, GEISA and TFMeCaSDa (VAMDC) databases.

Line intensities and self-broadening coefficients for the ν2 band of methyl chloride

The present report concerns measurements of lines intensities and self-broadening coefficients for 170 transitions of the ν2 band of both 12CH335Cl and 12CH337Cl isotopologues between 1291 and 1403cm−1. This work is the continuation of a previous effort on the ν5 band (Barbouchi Ramchani et al., 2013). For these studies, spectra of CH3Cl have been recorded at room temperature using a rapid scan Bruker IFS120 HR interferometer. The line parameters have been retrieved using a Voigt profile and a multispectrum fitting procedure. The average accuracy of the line parameters obtained in this work has been estimated to be between 2% and 5% for line intensities and between 5% and 10% for self-broadening coefficients depending on the transitions. A global comparison with the experimental values existing in the literature has been performed. The measurements of line intensities have also been compared to calculated values from HITRAN and GEISA databases.

New and improved infra-red absorption cross sections and ACE-FTS retrievals of carbon tetrachloride (CCl4)

Carbon tetrachloride (CCl4) is one of the species regulated by the Montreal Protocol on account of its ability to deplete stratospheric ozone. As such, the inconsistency between observations of its abundance and estimated sources and sinks is an important problem requiring urgent attention (Carpenter et al., 2014) [5]. Satellite remote-sensing has a role to play, particularly limb sounders which can provide vertical profiles into the stratosphere and therefore validate stratospheric loss rates in atmospheric models.This work is in two parts. The first describes new and improved high-resolution infra-red absorption cross sections of carbon tetrachloride/dry synthetic air over the spectral range 700–860cm−1 for a range of temperatures and pressures (7.5–760Torr and 208–296K) appropriate for atmospheric conditions. This new cross-section dataset improves upon the one currently available in the HITRAN and GEISA databases. The second describes a new, preliminary ACE-FTS carbon tetrachloride retrieval that improves upon the v3.0/v3.5 data products, which are biased high by up to ~20–30% relative to ground measurements. Making use of the new spectroscopic data, this retrieval also improves the microwindow selection, contains additional interfering species, and utilises a new instrumental lineshape; it will form the basis for the upcoming v4.0 CCl4 data product.

A spectroscopic database for water vapor between 5850 and 8340 cm−1

An accurate and complete empirical spectroscopic database is constructed for natural water in the 5850–8340cm−1 near infrared region (1.71–1.20µm). The global list includes more than 46,500 transitions of the six most abundant isotopologues (H216O, H218O, H217O, HD16O, HD17O, HD18O) in natural isotopic abundance with intensity greater than 1×10−29cm/molecule. All line positions were obtained by difference of empirically determined energy values. These empirical determinations are mostly based on extensive investigations of water vapor spectra by high-sensitivity CRDS complemented with literature data. In particular, the sets of energy levels of the minor isotopologues have been significantly enlarged from very recent analysis of CRDS spectra of D, 18O and 17O enriched water samples. The empirical line positions were associated to experimental intensity values from the literature obtained by FTS for the strong lines and CRDS for weaker lines. The list is made mostly complete by including a large number of weak transitions not yet detected, with empirical positions calculated from empirical levels associated with variational intensities. Air- and self-broadening coefficients and air-induced line shifts have been added to each transition using the most recent version of the algorithm used for the HITRAN and GEISA databases. Examples of comparison of CRDS spectra to simulations based on the HITRAN2012 list illustrate the advantages of our database.The relative merit of experimental and variational line intensities is discussed. A separate line list combining empirical line positions and variational intensities is provided. Future improvements from combination of experimental and variational intensities are suggested.

Spectroscopic line parameters of 12CH4 for atmospheric composition retrievals in the 4300–4500 cm−1 region

Due to the importance of methane as a trace atmospheric gas and a greenhouse gas, we have carried out a precise line-shape study to obtain the CH4–CH4 and CH4–air half-width coefficients, CH4–CH4 and CH4–air shift coefficients and off-diagonal relaxation matrix element coefficients for methane transitions in the spectral range known as the “methane Octad”. In addition, the associated temperature dependences of these coefficients have been measured in the 4300–4500cm−1 region of the Octad. The high signal to noise ratio spectra of pure methane and of dilute mixtures of methane in dry air with high resolution have been recorded at temperatures from 148K to room temperature using the Bruker IFS 125 HR Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory, Pasadena, California. The analysis of spectra was done using a multispectrum non-linear least-squares curve fitting technique. Theoretical calculations have been performed and the results are compared with the previously published line positions, intensities and with the line parameters available in the GEISA and HITRAN2012 databases.

Spectral distortion of dual-comb spectrometry due to repetition rate fluctuation**Project supported by the State Key Laboratory of Precision Measurement Technology & Instruments of Tsinghua University and the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61205147).

Dual-comb spectrometry suffers the fluctuations of parameters in combs. We demonstrate that the repetition rate is more important than any other parameter, since the fluctuation of the repetition rate leads to a change of difference in the repetition rate between both combs, consequently causing the conversion factor variation and spectral frequency misalignment. The measured frequency noise power spectral density of the repetition rate exhibits an integrated residual frequency modulation of 1.4 Hz from 1 Hz to 100 kHz in our system. This value corresponds to the absorption peak fluctuation within a root mean square value of 0.19 cm−1 that is verified by both simulation and experimental result. Further, we can also simulate spectrum degradation as the fluctuation varies. After modifying misaligned spectra and averaging, the measured result agrees well with the simulated spectrum based on the GEISA database.

Line position and line intensity analyses of the high-resolution spectrum of H218O up to the First Triad and [formula omitted

Line position and line intensity analyses of the high-resolution spectrum of the H218O isotopic species of the water molecule are performed with the Bending-Rotation approach up to J=17 and the First Triad of interacting states, (020), (100), and (001). The line position analysis involves microwave and terahertz transitions, ground state combination differences, far infrared and infrared lines, and experimental energy levels which were reproduced with a 1.2 unitless standard deviation. The data set considered in the line intensity analysis consists of 3707 infrared transitions recorded using absorption spectroscopy at room temperature which were fitted with a 1.4 unitless standard deviation. The results of both analyses are compared with previous investigations and are used to build a line position and line intensity database to update the HITRAN and GEISA databases. A comparison with the HITRAN 2012 database reveals that the new database yields intensity values closer to the experimental ones.

New and improved infrared absorption cross sections for dichlorodifluoromethane (CFC-12)

Abstract. Despite its widespread commercial use throughout the twentieth century, primarily in the refrigeration industry, dichlorodifluoromethane (CFC-12) is now known to have the undesirable effect of depleting stratospheric ozone. As this long-lived molecule slowly degrades in the atmosphere, monitoring its vertical concentration profile using infrared sounders on satellite platforms crucially requires accurate laboratory spectroscopic data. This work describes new high-resolution infrared absorption cross sections of dichlorodifluoromethane over the spectral range 800–1270 cm−1, determined from spectra recorded using a high-resolution Fourier transform spectrometer (Bruker IFS 125HR) and a 26 cm pathlength cell. Spectra of dichlorodifluoromethane/dry synthetic air mixtures 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 (7.5–761 Torr and 190–294 K) appropriate for atmospheric conditions. This new cross-section dataset improves upon the one currently available in the HITRAN and GEISA databases.