Temperature dependence of self- and N2-broadeningand pressure-induced shifts in the 3←0 band of CO

Abstract

A variable-temperature single-pass absorption gas cell with an optical pathlength of 147.5 cm was designed and built for spectroscopic measurements of gases of atmospheric interest. The cell is optically matched to a Bomem DA8.3 Fourier transform spectrometer. A heating/cooling system enveloping the cell, used together with a Neslab ULT-80 thermal bath, allows spectroscopic studies of gas samples at temperatures ranging from 205 to 350 K and at pressures up to 1 atm. Tests of the optical, thermal, and vacuum operation of the system were performed. Spectra of the 3ˆ0 vibrational -rotational band of carbon monoxide were recorded from 225 to 348 K and used to determine the rotational gas temperatures. These results were compared with values obtained using thermocouples, in order to assess the thermal performance of the new system. A second temperature-controlled cell 25-cm long, able to withstand pressures up to 30 atm, was also used to record CO spectra. We have recorded high-resolution FTIR spectra of CO and CO perturbed by N 2 at temperatures from 295 to 348 K. The spectra were analyzed to determine pressure broadening and pressure-induced shift coefficients, along with their temperature dependence for several transitions in the second overtone band of CO. The results, especially for self-broadening, are in excellent agreement with other recent measurements reported in the literature. q

Collisional line shifting and broadening in the fundamental P-branch of CO in Ar between 214 and 324K

“…(The other two studies in the CO fundamental band [6,8], did not consider any temperature scaling law for their measured shifting coefficients.) Unlike Predoi-Cross et al [21], we find that the linear law, Eq. (2), does not represent our results.…”

“…Predoi-Cross et al [21] considered two empirical temperature scaling laws for their measured shifting coefficients in the 3 ‹ 0 band of CO-CO and CO-N 2 between 296 and 348 K. The first was a simple linear law…”

“…This power law was also used in the CO fundamental band study by Sung and Varanasi [7] and in an earlier methane study by Varanasi and Chudamani [22]. Unfortunately, none of [7,21,22] discusses how well Eq. (3) represents the measured temperature dependence, although they do report values of n 0 (typically between 0.8 and 1.5) with accuracies between about ±0.1 and ±0.3.…”

“…There have been several papers that have reported CO broadening coefficients with estimated errors near ±5 · 10 À5 cm À1 /atm, but have used an aL [5,11,21] or SDHC [10,26] model to obtain them. The models discussed here have also been used for many other gases, and there are many similar models in use (e.g., Galatry, speed-dependent Galatry, speed-dependent asymmetric Voigt) that are subject to the same error considerations.…”

Self-broadening and -shifting of very intense lines of the 1←0 band of 12 C 16 O

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] and those therein). Nevertheless, while many measurements have been made in the 2'0 [3][4][5][6][7] and 3'0 [7][8][9][10][11][12][13][14] overtone bands, much less attention has been paid to the fundamental band [1,2], likely due to the very strong transition moment for this 1'0 band. Indeed, at pressures where the line shape is dominated by intermolecular collisions (Lorentzian regime) the absorption coefficient at the center of the R(7) line of pure 12 C 16 O is about 50 cm À 1 [15].…”