Gh. Blanquet

Determination of broadening coefficients and intensities for overlapping spectral lines with application to the QR (3,K) lines in the v3 band of CH353Cl

Abstract We have developed a method of extracting individual line parameters from overlapping absorption spectra recorded with a tunable diode-laser spectrometer. Assuming Voigt profiles for the individual lines, the overall absorption is expressed as the sum of the absorption coefficients of the recorded lines plus a small contribution due to neighboring lines. The computational procedure has been applied to the four Q R (3, K ) lines, self-broadened and broadened by N 2 ,O 2 , Ar and He, in the v 3 band of CH 35 3 Cl at 736.3 cm -1 . The intensities and collision-broadened widths are found to be linear functions of the broadener pressures, which implies negligible line-mixing effects between the K components. For all the perturbers considered the broadening coefficients of the Q R (3, K lines decrease significantly as K increases, in agreement with theoretical results.

Diode laser measurements of line strengths and collisional half-widths in the ν1 band of OCS at 298 and 200K

Abstract Absolute line strengths and self-broadened half-widths have been measured at 298 and 200 K for spectral lines ranging from J = 1 to 55 in the ν1 band (860 cm-1) of 16O12C32S, using a tunable diode laser spectrometer. The vibrational transition moment (6.412 ± 0.16 × 10-2D) as well as the absolute intensity (29.63±1.48 cm-2-atm-1 at 298 K), of the ν1 band are determined from these line-strenght measurements. By applying two semi-classical impact theories of collisional broadening, we have obtained results for half-widths at 298 and 200 K which are significantly larger than the experimental data for |m|

Line-mixing effects in N2O Q branches: Model, laboratory, and atmospheric spectra

A model based on the energy corrected sudden approximation is used in order to account for line-mixing effects in N2O Q branches of Σ↔Π bands. The performance of this theoretical approach is demonstrated by comparisons with many (about 70) N2O–N2 and N2O–O2 laboratory spectra recorded in the 5 and 17 μm regions by three instrument setups; the Q branches of the 2ν20e–ν21f (near 579.3 cm−1), ν2 (near 588.8 cm−1), and ν2+ν3 (near 2798.3 cm−1) bands are investigated for different pressures (0.1–2.0 atm) and temperatures (200–300 K). The model is used to generate a set of line-mixing parameters for the calculation of the absorption by the ν2 Q branch under atmospheric conditions. These data are tested by comparisons between computed stratospheric emissions and values measured using a balloon-borne high resolution Fourier transform instrument. The results confirm the need to account for the effects of line mixing and demonstrate the capability of the model to represent the N2O absorption in a region which can b...

Pressure broadening study at low temperature: application to methane.

We studied the R(0) line profile in the CH4 v4 band from room temperature to 188 K with N2 as a perturber, to 100 K with O2 as perturber, and from room temperature to 15 K using He as a perturber. The N2 and O2 measurements were performed over a total pressure range of 15-110 mbar, and for the He measurements the maximum sample pressure at 15 K was 1.10 mbar. Broadening parameters were determined, taking into account the confinement narrowing (Dicke effect), and narrowing parameters, deduced from the soft or hard collision model, are compared with the dynamic friction coefficient calculated values. We also obtained preliminary values for the temperature dependence of the N2, O2 and He line broadening parameters for this transition.

SIMPLE MODELLING OF Q-BRANCH ABSORPTION. II: APPLICATION TO MOLECULES OF ATMOSPHERIC INTEREST (CFC-22 AND CH3CL)

Abstract The simple approach developed in a previous paper in order to model absorption by Q-branches is applied to the 2v6 Q-branch of CFC-22 perturbed by N2 and to the v5R Q0-branch of CH3Cl perturbed by He. Measurements have been made for these two systems at room temperature for a number of pressures in the 0.05–1.00 atm range. It is shown that our model enables satisfactory prediction of both the pressure and wavenumber dependences of absorption with only six effective parameters; the latter, which depend on temperature only, have been deduced from measured spectra. There values are in satisfactory agreement with results from other sources, except for the average broadening parameter, which is generally underestimated with the model as explained in our previous paper.

Line‐mixing effects in Ar‐broadened doublets of a hot band of OCS

The spectra of several Ar‐broadened symmetric doublets in the hot band ν1+ν2−ν2 (at 850 cm−1) of OC 32S have been recorded with a tunable diode‐laser spectrometer. The pressure‐broadening coefficients measured for sufficiently separated lines belonging to 7 doublets are in agreement with the results previously obtained in the ν1 band. From these data, we have determined, for different pressures of argon, line‐coupling coefficients for 15 doublets in the P and R branches of the hot band. These coefficients appear to be small and negative, at the limit of our estimated accuracy, which implies very weak line‐mixing effects in the doublets, in agreement with the results of a semiclassical calculation as well as with results of coupling cross sections estimated at large‐j values from the infinite order sudden (IOS) approximation.

Diode-laser measurements of He- and N2-broadening coefficients and line-mixing effects in the Q-branch of the ν1–ν2 band of CO2

Abstract He- and N 2 -broadening coefficients have been measured for the lines Q 2 to Q 22 of the v 1 - v 2 (10 0 01 ← 01 1 01) band of CO 2 near 720.80 cm −1 , using a tunable diode-laser spectrometer. The collisional widths have been obtained at low perturber pressures by fitting Voigt and Galatry profiles to the measured shapes of the lines. Spectra in the v 1 - v 2 band of CO 2 in mixture with He and N 2 have also been recorded at higher pressures. The deviations observed from an additive superposition of Lorentzian lines have been notably reduced by considering collision-induced line-mixing effects.

Spectral intensities in the 2ν20 band of carbonyl sulfide

Mesure de 52 raies de OCS correspondant aux branches P et R et a des valeurs de 5 comprises entre 1 et 71

Simple modelling of Q-branch absorption—III. Pressure, temperature, and perturber dependences in the 2v6 Q -branch of 12CH35ClF2 (HCFC-22)

Abstract The simple approach developed in a previous paper in order to model absorption by Q-branches is applied to the 2v6 Q-branch of 12CH35ClF2 (HCFC-22). Measurements have been made using a tunable diode laser for pure HCFC-22 and mixtures with N2 and O2. The pressures and temperatures investigated, which are suitable for atmospheric applications, range from 0.05 to 1.0 atm and from 200 to 300 K, respectively. It is shown that our model enables satisfactory prediction of both the pressure, temperature, and wavenumber dependences of absorption with eleven effective parameters which have been deduced from measured spectra. Their values are in satisfactory agreement with results from other sources. The model proposed can also accurately predict spectra measured by other authors as well as correctly compute atmospheric transmission.