To accurately attribute sources and sinks of molecules like CO_{2}, remote sensing missions require line intensities (S) with relative uncertainties u_{r}(S)<0.1%. However, discrepancies in S of ≈1% ...are common when comparing different experiments, thus limiting their potential impact. Here we report a cavity ring-down spectroscopy multi-instrument comparison which revealed that the hardware used to digitize analog ring-down signals caused variability in spectral integrals which yield S. Our refined approach improved measurement accuracy 25-fold, resulting in u_{r}(S)=0.06%.
We present a new measurement of the 1S-3S two-photon transition frequency of hydrogen, realized with a continuous-wave excitation laser at 205 nm on a room-temperature atomic beam, with a relative ...uncertainty of 9×10^{-13}. The proton charge radius deduced from this measurement, r_{p}=0.877(13) fm, is in very good agreement with the current CODATA-recommended value. This result contributes to the ongoing search to solve the proton charge radius puzzle, which arose from a discrepancy between the CODATA value and a more precise determination of r_{p} from muonic hydrogen spectroscopy.
•Accurate CO2 transition intensities were measured near λ = 2.06 µm by FS-CRDS.•The relative combined standard uncertainty for all measured intensities is 0.08 %.•Comparisons with existing databases ...revealed systematic biases as large as 1 %.•We scaled the ab initio DMS of Zak et al. to yield Sband626 = 7.183 × 10−21 cm molecule−1.•Results constrained the Herman-Wallis expansion, with an RMSD of σ^ = 0.18 %.
The λ = 2.06 µm absorption band of CO2 is widely used for the remote sensing of atmospheric carbon dioxide, making it relevant to many important top-down measurements of carbon flux. The forward models used in the retrieval algorithms employed in these measurements require increasingly accurate line intensity and line shape data from which absorption cross-sections can be computed. To overcome accuracy limitations of existing line lists, we used frequency-stabilized cavity ring-down spectroscopy to measure 39 transitions in the 12C16O2 absorption band. The line intensities were measured with an estimated relative combined standard uncertainty of ur = 0.08 %. We predicted the J-dependence of the measured intensities using two theoretical models: a one-dimensional spectroscopic model with Herman-Wallis rotation-vibration corrections, and a line-by-line ab initio dipole moment surface model Zak et al. JQSRT 2016;177:31-42. For the second approach, we fit only a single factor to rescale the theoretical integrated band intensity to be consistent with the measured intensities. We find that the latter approach yields an equally adequate representation of the fitted J-dependent intensity data and provides the most physically general representation of the results. Our recommended value for the integrated band intensity equal to 7.183 × 10−21 cm molecule−1 ± 6 × 10−24 cm molecule−1 is based on the rescaled ab initio model and corresponds to a fitted scale factor of 1.0069 ± 0.0002. Comparisons of literature intensity values to our results reveal systematic deviations ranging from −1.16 % to +0.33 %.
The 12 CO 2 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 30 013-0 0 0 01 band of 12 CO 2 in air are studied with a cavity ring down spectrometer (CRDS). For each transition, high signal-to-noise ratio spectra (between 20 0 0 and 20 0 0 0) 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).
High resolution spectroscopy of the hydrogen atom takes on particular importance in the new SI, as it allows to accurately determine fundamental constants, such as the Rydberg constant and the proton ...charge radius. Recently, the second most precisely measured transition frequency in hydrogen, 1S−3S, is obtained by our group. In the context of the Proton Radius Puzzle, this result calls for further investigation.
High resolution spectroscopy of the 1S–3S transition of the hydrogen atom at 300 K has been achieved at LKB, Paris, with an uncertainty of 9e‐13. The deduced value of the proton radius is in good agreement with the latest Codata adjustment. It however disagrees with the value from muonic hydrogen spectroscopy, as with other recent results.
•High-precision, low-uncertainty CRDS measurements of 1.27 µm air-broadened O2 band line with frequency axis linked to Cs clock.•New line list reported using Dicke-narrowing constrained Hartmann-Tran ...profile.•Multi-spectrum line shape analysis and Monte Carlo model indicates strong numerical correlation between Dicke narrowing and speed dependent narrowing mechanisms.•Intensities and broadening coefficients measured with relative uncertainties of 0.15 % and 0.05 %, respectively and line positions measured with 60 kHz uncertainty.•Measurements values of binary absorption coefficients for collision induced absorption spectrum in sub-percent-level agreement with prior work.
We present broadband spectroscopic parameters in the a1Δg−X3Σg−(0,0) band of 16O2 centered near 1.27 µm. High-fidelity absorption spectra were acquired on room-temperature air samples over the pressure range of 3.3 kPa to 100 kPa using a length-stabilized cavity ring-down spectrometer, with spectrum frequencies linked to a Cs clock via an optical frequency comb. Parameters were determined by multi-spectrum fitting of advanced line profiles to the measured spectra. This analysis yielded line intensities, positions, collisional broadening and shifting coefficients, Dicke narrowing and speed dependent line shape parameters, first-order line mixing coefficients, and O2-air binary absorption coefficients for collision-induced absorption. We report relative standard uncertainties in the line intensities and broadening coefficients of 0.16 % and 0.05 %, respectively, and line position uncertainties of 60 kHz (2 × 10−6 cm−1). Our analysis reveals strong numerical correlation in fits of the Dicke narrowing and speed dependent widths and shows that inclusion of a recently proposed modification to the Hartmann Tran line profile can increase fitted Dicke narrowing frequencies by as much as 50 %.
The accurate knowledge of the water vapor absorption in the 10 µm atmospheric window is of strong importance because this spectral range coincides with the maximum black body emission of Earth. ...Presently, the water vapor self-continuum is measured at the 1185 cm−1 (8.45 µm) spectral point, located in the most transparent interval of the 10 µm window. Measurements are performed at four temperatures ranging from 296 to 308 K using a newly developed Optical Feedback Cavity Ring Down Spectrometer (OF-CRDS). Self-continuum cross-sections, CS, are derived from the pressure dependence of the absorption during pressure ramps of pure water vapor up to 18 mbar. From the quadratic pressure dependence observed for the absorption coefficient at each temperature, we derived the value of the cross-section (Cs=0.996(12) × 10−22 cm2molecule−1atm−1 at 296 K) and its temperature dependence. These results are discussed in relation with previous literature measurements available in the 10 µm window. Our cross-section is found about 20% smaller than the MT_CKD_4.1 value and the available experimental works seem to indicate that the MT_CKD_4.1 temperature dependence is overestimated.
•First laboratory detection of electric quadrupole rovibrational transitions in CO2.•High sensitivity optical-feedback-cavity enhanced absorption spectroscopy (OFCEAS) in the 3.3 µm transparency ...window of CO2.•The ν2+ν3 band of 12C16O2 involves both electric-quadrupole (E2) and magnetic-dipole (M1) contributions.•Good agreement with ab initio predictions of the electric-quadrupole line intensities.•E2 and M1 transitions are missing in spectroscopic databases while their intensities can be above the electric-dipole line intensity cut-off.
The recent detections of electric-quadrupole (E2) transitions in water vapor and magnetic-dipole (M1) transitions in carbon dioxide have opened a new field in molecular spectroscopy. While in their present status, the spectroscopic databases provide only electric-dipole (E1) transitions for polyatomic molecules (H2O, CO2, N2O, CH4, O3…), the possible impact of weak E2 and M1 bands to the modeling of the Earth and planetary atmospheres has to be addressed. This is especially important in the case of carbon dioxide for which E2 and M1 bands may be located in spectral windows of weak E1 absorption. In the present work, a high sensitivity absorption spectrum of CO2 is recorded by Optical-Feedback-Cavity Enhanced Absorption Spectroscopy (OFCEAS) in the 3.3 µm transparency window of carbon dioxide. The studied spectral interval corresponds to the region where M1 transitions of the ν2+ν3 band of carbon dioxide were recently identified in the spectrum of the Martian atmosphere. Here, both M1 and E2 transitions of the ν2+ν3 band are detected by OFCEAS. Using recent ab initio calculations of the E2 spectrum of 12C16O2, intensity measurements of five M1 lines and three E2 lines allow us to disentangle the M1 and E2 contributions. Indeed, E2 intensity values (on the order of a few 10–29 cm/molecule) are found in reasonable agreement with ab initio calculations while the intensity of the M1 lines (including an E2 contribution) agree very well with recent very long path measurements by Fourier Transform spectroscopy. We thus conclude that both E2 and M1 transitions should be systematically incorporated in the CO2 line list provided by spectroscopic databases.
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The
= 2.06 μm absorption band of CO
is widely used for the remote sensing of atmospheric carbon dioxide, making it relevant to many important top-down measurements of carbon flux. The forward models ...used in the retrieval algorithms employed in these measurements require increasingly accurate line intensity and line shape data from which absorption cross-sections can be computed. To overcome accuracy limitations of existing line lists, we used frequency-stabilized cavity ring-down spectroscopy to measure 39 transitions in the
C
O
absorption band. The line intensities were measured with an estimated relative combined standard uncertainty of
= 0.08 %. We predicted the
-dependence of the measured intensities using two theoretical models: a one-dimensional spectroscopic model with Herman-Wallis rotation-vibration corrections, and a line-by-line
dipole moment surface model Zak et al. JQSRT 2016;177:31-42. For the second approach, we fit only a single factor to rescale the theoretical integrated band intensity to be consistent with the measured intensities. We find that the latter approach yields an equally adequate representation of the fitted
-dependent intensity data and provides the most physically general representation of the results. Our recommended value for the integrated band intensity equal to 7.183 × 10
cm molecule
± 6 × 10
cm molecule
is based on the rescaled
model and corresponds to a fitted scale factor of 1.0069 ± 0.0002. Comparisons of literature intensity values to our results reveal systematic deviations ranging from -1.16 % to +0.33 %.
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