Temperature Dependence of the Collision‐Induced Absorption Band of O₂ Near 1.27 µm

Abstract

The 1.27 μm O2 band is increasingly called upon for air‐mass determination from ground‐based and space‐borne atmospheric spectra because of its spectral proximity to CO2, and CH4 bands at 1.6 μm, in contrast to the more distant A‐band at 0.76 μm. For this purpose, it is important to well characterize not only the narrow absorption lines but also the strong underlying broad collision‐induced absorption (CIA) structure and its temperature dependence. Spectra of pure O2, and of O2 in N2, were recorded by cavity ring down spectroscopy (CRDS) at 271 K and 332 K, with the help of a newly developed temperature regulated cell. The quality of the spectra allowed determining the small variations (at the few percent level) of the BO2−O2, BO2−N2, and BO2−air binary coefficients with temperature. Together with the binary coefficients at 297 K reported previously, they allow characterizing the temperature dependence of the O2 CIA at 1.27 µm in atmospheric conditions. The obtained results are compared with previous measurements by Fourier transform spectroscopy (FTS) and recent theoretical calculations. In the wings of the O2‐O2 CIA, an increase with temperature is observed in agreement with calculations but contrary to these calculations, a decrease is observed near the maximum of the CIA band. The temperature dependence is found in good agreement with the theoretical BN2−O2values and the experimental BO2−air values derived from the FTS measurements. Binary coefficients integrated over the entire band show almost no variation with temperature for O2‐N2 and a small increase for pure O2, in agreement with the theoretical predictions.

CRDS measurements of air-broadened lines in the 1.6 µm band of 12CO2: Line shape parameters with their temperature dependence

“…Most of the light is coupled into a temperature stabilized high finesse cavity (TS-HFC) described in [22] where ring down (RD) events are achieved at resonance by switching the laser light off with an acousto-optic modulator (AOM). The extinction coefficient, (), is deduced from: (1) where  and  0 are the RD times for the cell filled with the gas mixture and evacuated, respectively, c is the speed of light and n is the refractive index of the absorbing gas.…”

“…Two versions of the TS-HFC, described in [20] and [22], are used here, namely the V1 (FSR= 258 MHz; F~ 211600) and the improved V2 (FSR= 332 MHz; F~ 310600) versions. Both work on the same principle (see Fig.…”

“…1 of Ref. [22]): a fluid, whose temperature is regulated using a deported refrigerated/heating circulator (model Corio 1000F from Julabo), flows through two counterpropagating copper coils wrapped around a tube containing the two dielectric mirrors of the cavity.…”

“…Plotting the retrieved parameters γ 0 (T), cm -1 atm -1 cm -1 atm -1 cm -1 atm -1 K -1 cm -1 atm -1 atm -1 R(6) 0.08295(3) 0.698(4) -0.00465(3) 0.0000107(10) 0.00211 (22) 0.8(9) 0.0889(12) 0.66(10) 0.093(5) 0.01040(49) 0.1(4) R(12) 0.07726(1) 0.682(2) -0.00506(2) 0.0000128 (7) 0.00218( 5 Table 2. List of the spectroscopic parameters obtained for the five transitions studied in this work.…”

Characterization of the H2O+CO2 continuum within the infrared transparency windows

“…The CRDS and OFCEAS techniques have proven their ability to measure weak absorption continua for pure H 2 O (see for example [12,13,14]), O 2 [15,16], CO 2 [17,18,19] and H 2 O in air [20] gas samples. In this work, we applied our CRDS and OFCEAS spectrometers to the determination of the H 2 O+CO 2 continuum in the 3.5 µm, 2.3 µm and 1.6 µm transparency windows.…”