•Water self-continuum cross-sections are measured at 30 and 47°C, by OFCEAS at 2853 cm−1•Water foreign-continuum cross-sections are measured at 34 and 47°C, by OFCEAS at 4302 cm−1•These accurate ...measurements are consistent with previous OFCEAS and CRDS studies in the 4.0 and 2.1 µm window•Significant underestimations of the MT_CKD_V3.5 foreign-continuum in the center of the 2.1 µm window is confirmed
Measurements of the water vapor absorption cross-sections at two spectral points of the 2.1 µm and 4.0 µm transparency windows are performed by optical feedback cavity enhanced absorption spectroscopy (OFCEAS).
The self-continuum cross-section, CS, is measured for temperature values of 30 and 47°C (303 and 320 K) at the 2853 cm−1 spectral point, corresponding to the lowest opacity region of the 4.0 µm transparency window. The CS values derived from the pressure squared dependence of the self-continuum, are found consistent with previous CEAS measurements in the considered window but significantly smaller than measurements by Fourier transform spectroscopy (FTS). The CS temperature dependence is discussed in relation with FTS measurements at high temperature.
Foreign-continuum cross-sections, CF, are newly obtained from OFCEAS spectra of moist air in flow regime at the 4302 cm−1 spectral point of the low energy edge of the 2.1 µm window. After subtraction of the monomer and self-continuum contributions, CF values are derived from the linear variation of the foreign-continuum absorption with the product of the water vapor and air partial pressures. The measurements were performed for temperature values of 34 and 47°C (307 and 320 K) and no significant temperature dependency was observed. The present CF value at 4302 cm−1 is gathered with previous CEAS measurements at seven spectral points of the 2.1 µm window. This consistent set of CF values is used to derive from a polynomial fit, the empirical frequency dependence of CF(ν) over the 4250-5000 cm−1 range. Overall, the semi-empirical MT_CKD_3.5 values of CF are significantly underestimated in the centre of the considered window.
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Simultaneous collision-induced transitions in H2O+CO2 gas mixtures Fleurbaey, H.; Mondelain, D.; Fakhardji, W. ...
Journal of Quantitative Spectroscopy & Radiative Transfer/Journal of quantitative spectroscopy & radiative transfer,
July 2022, 2022-07-00, 2022-07, Volume:
285
Journal Article
Peer reviewed
Open access
•Absorption spectra of CO2+H2O mixtures are measured by CRDS in the 1.6 µm window.•A collision induced absorption (CIA) band is found to contribute to the continuum near 6000 cm−1.•The observed CIA ...is assigned to simultaneous excitations of CO2 and H2O in the ν3 antisymmetric and ν1 symmetric stretching modes, respectively.•The assignment is confirmed by the isotopic shift of the CIA in 13CO2+H2O mixtures.•Classical molecular dynamics simulations of the considered CIA agree with the observations.
A collision induced absorption (CIA) band has been measured near 6000 cm−1 in a spectrum of humidified CO2 recorded by cavity ring down spectroscopy (CRDS) at low pressure (<1 atm). This absorption adds a contribution to the H2O+CO2 continuum mostly originating from far wings of the CO2 and H2O resonance lines broadened by collisions with H2O and with CO2, respectively. The observed CIA corresponds to a simultaneous excitation of 12CO2 and H2O colliding molecules in the ν3 antisymmetric and ν1 symmetric stretching mode, respectively. CRDS spectra recorded near 5940 cm−1 with a highly enriched 13CO2 sample provide a confirmation of the assignment since the measured CIA isotopic spectral shift (of about −68 cm−1) coincides with that between the ν3 bands of 12CO2 and 13CO2. The integrated binary coefficient of the two CIA is evaluated and found to be on the order of 2.3 × 10−3 cm−2amagat−2. Classical molecular dynamics simulations (CMDS) of the considered CIA are also presented, based on the dominant dipole induction mechanism associated with the vibrational matrix elements of the dipole of CO2 (ν3) and isotropic polarizability of H2O (ν1). The results of the calculations are found in good agreement with the observations, thus further validating the attribution of the observed CIA structure to the above mentioned double transitions.
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•The line shapes of four transitions of the 12CO2 in the 2 µm region are studied.•High S/N spectra are recorded for CO2 in air by CRDS between 245 and 330 K.•A multi-spectrum fit procedure with SDNG ...profiles and line-mixing has been used.•Accurate line profile parameters and their temperature dependence are obtained.•Results are compared with previous experimental data and rCMD simulations.
The 20013–00001 and 20012–00001 bands of 12C16O2 in the 2 µm region are used by many instruments on-board satellites and in ground-based networks to monitor the CO2 column-averaged dry air mole fraction in the Earth's atmosphere. An accurate knowledge of the corresponding spectroscopic parameters and their temperature dependence is thus needed to map sources and sinks of carbon dioxide. In this work, we retrieve the line-shape parameters and their temperature dependence exponents/coefficients for the P(16) and P(28) transitions of the 20012–00001 band, and the R(24) and R(30) transitions of the 20013–00001 band. These parameters are obtained from a multi-spectrum fit procedure using a speed-dependent Nelkin-Ghatak profile including the line-mixing effect in its first-order approximation. High signal-to-noise spectra (quality factor between typically 3000 and 6000) are recorded at different conditions of pressure (from 50 to 750 Torr) and temperature (from 245 to 330 K) for mixtures of CO2 in air using a comb-assisted cavity ring down spectrometer with a temperature stabilized high finesse cavity. Air-broadening coefficients are measured with an estimated uncertainty better than 0.1% and absolute frequencies of the transitions are obtained with uncertainty better than 100 kHz. The determined line-shape parameters are consistent with previous values derived in the 1.6 µm region confirming the absence of significant vibrational dependence (except for the air-pressure shift coefficient). The retrieved parameters agree well with literature values by Fourier transform spectroscopy and classical molecular dynamic simulations. The parameters of the speed-dependent Voigt profiles provided by the HITRAN2020 database are mostly validated. The comparison to the CO2 line parameters adopted for the OCO missions is discussed.
A collision induced absorption (CIA) band has been measured near 6000 cm$^{-1}$ in a spectrum of humidified CO$_2$ recorded by cavity ring down spectroscopy (CRDS) at low pressure (<1 atm). This ...absorption adds a contribution to the H$_2$O+CO$_2$ continuum mostly originating from far wings of the CO$_2$ and H$_2$O resonance lines broadened by collisions with H$_2$O and with CO$_2$, respectively. The observed CIA corresponds to a simultaneous excitation of 12 CO$_2$ and H$_2$O colliding molecules in the $\nu_3$ antisymmetric and $\nu_1$ symmetric stretching mode, respectively. CRDS spectra recorded near 5940 cm$^{-1}$ with a highly enriched $^{13}$CO$_2$ sample provide a confirmation of the assignment since the measured CIA isotopic spectral shift (of about-68 cm$^{-1}$) coincides with that between the $\nu_3$ bands of $^{12}$CO$_2$ and $^{13}$CO$_2$. The integrated binary coefficient of the two CIA is evaluated and found to be on the order of 2.3×10$^{-3}$ cm$^{-2}$ amagat$^{-2}$. Classical molecular dynamics simulations (CMDS) of the considered CIA are also presented, based on the dominant dipole induction mechanism associated with the vibrational matrix elements of the dipole of CO$_2$ ($\nu_3$) and isotropic polarizability of H$_2$O ($\nu_1$). The results of the calculations are found in good agreement with the observations, thus further validating the attribution of the observed CIA structure to the above mentioned double transitions.
The 12CO2 band at 1.6 µm is used for carbon dioxide monitoring in the Earth atmosphere. The targeted accuracy of these measurements motivates important efforts to improve the quality of the ...spectroscopic parameters in atmospheric conditions. In the present work, the line shapes of the R(6), R(12), R(16), R(18) and R(20) transitions of the 30013-00001 band of 12CO2 in air are studied with a cavity ring down spectrometer (CRDS). For each transition, high signal-to-noise ratio spectra (between 2000 and 20000) are recorded at different temperatures (250, 274, 285, 295 and 320 K) and total pressures (50, 100, 250, 500 and 750 Torr). To this end, a spectrally narrowed and stable (sub-kHz) laser source is coupled into a temperature regulated high-finesse optical cavity. The frequency scale of each spectrum is accurately determined from measurements of the frequency of the beat note between a part of the laser light and the closest tooth of a frequency comb referenced to a rubidium clock. A multi-spectrum fit procedure with quadratic speed dependent Nelkin-Ghatak profiles, including line-mixing effects, has been used to derive for each transition, the different spectroscopic parameters and their temperature dependence. Results are discussed in comparison with previous experimental data, HITRAN2020 database and values obtained from requantized classical molecular dynamics simulations (rCMDS).
