High sensitivity spectroscopy of the O2 band at 1.27 µm: (II) air-broadened line profile parameters

Abstract

A cavity ring down spectrometer referenced to a frequency comb is used to study the profile of air-broadened O2 lines of the 1.27 µm band. To this aim, spectra of O2 in dry air and of O2 in N2 with 2% of O2 were measured, respectively in the 7720-7920 cm−1 and 7868-7887 cm-1 spectral ranges at room temperature and various pressures ranging from 50 to 700 Torr. Detailed line profile analysis is reported for 85 transitions using the speed dependent Nelkin-Ghatak model and a multi-spectrum treatment of the two series of spectra. Line mixing was found necessary to be taken into account in the analysis of lines in the region of the Q branch. The derived line parameters including the broadening and shifting coefficients, the speed dependent components of the collisional line broadening and shifting, as well as the Dicke narrowing parameter are discussed and compared to literature data. In particular, the speed dependence components of the collisional broadening are found to agree satisfactorily with predictions obtained by molecular dynamic simulations. This obtained set of line-shape parameters should allow for improved modeling of atmospheric spectra in the 1.27 um spectral region.

Line-shape parameters and their temperature dependences predicted from molecular dynamics simulations for O2- and air-broadened CO2 lines

“…[12,40,42] used the speed-dependent Voigt profile while the speed-dependent Nelkin-Ghatak profile is used in the present work to retrieve line-shape parameters. The speed dependence parameter obtained with the sdV profile is usually larger than that obtained using the sdNG or HT profile, as observed in [38,43,45,46] for instance. Note that in [12,40,42], the ratio / was assumed to be independent of T, as in [13].…”

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

“…The reported line parameters were retrieved from low pressure (0.67 kPa and 1.34 kPa) spectra of pure O2 measured with a CRDS setup based on an extended cavity diode laser (ECDL) and coupled to a self-referenced frequency comb using the quadratic speed-dependent Nelkin-Ghatak profile (qsdNG). A CRDS setup using a series of distributed feedback laser diodes and referenced to the same frequency comb was used to record air-and N2-broadened spectra of O2 in the 7800-7912 cm -1 region corresponding to the B4 band of MicroCarb [25]. Line intensities and lineshape parameters were retrieved for 85 O2 magnetic lines using the qsdNG model [25].…”

“…A CRDS setup using a series of distributed feedback laser diodes and referenced to the same frequency comb was used to record air-and N2-broadened spectra of O2 in the 7800-7912 cm -1 region corresponding to the B4 band of MicroCarb [25]. Line intensities and lineshape parameters were retrieved for 85 O2 magnetic lines using the qsdNG model [25]. Linemixing (LM) between lines in the Q branch was taken into account with the use of the first order line-mixing approximation [26].…”

“…Compared to the HITRAN2016 and GEISA2015 lists, significant differences between the line positions, intensities and shape parameters have been pointed out in these recent CRDS studies (see [24,25] for instance). In the present work, different spectroscopic datasets of the ∆ − Σ (0 − 0) band [5,11,19,24,25,27] are tested by comparing ground-based atmospheric transmission measurements (TCCON spectra) with spectra calculated using the Spectroscopic Parameters And Radiative Transfer Evaluation (SPARTE) chain [28]. The TCCON spectra were chosen for these validation tests since they provide a high signal-to-noise ratio and high resolution together with well-known pressure, temperature and humidity conditions as well as instrument characteristics (see [3] and references therein).…”

“…Comparisons between calculated and measured atmospheric spectra are then discussed in Section 3, before some concluding remarks and directions for future studies (Section 4). The first one, hereafter called "Tran2020", includes data from Tran et al [25] from 7784.8 cm -1 to 7915.8 cm -1 retrieved from CRDS spectra recorded for a large pressure range from 6.7 to 94 kPa (50 to 700 Torr) and fitted with the qsdNG profile. For Q branch lines, first order line-mixing (LM) effects were also taken into account.…”