V. Menoux

Line shape in the low-frequency wing of self-broadened CO 2 lines

The shape of the far wings of self-broadened CO(2) lines has been investigated in the spectral region (2140-2250 cm(-1).), i.e., on the low wavenumber side of the lines of the most intense band (upsilon(3) of(12)C(16)O(2)). The experimental results have been compared to calculated values based on the AFGL 1982 compilation. From this comparison it appears that the wings of the lines on the low wavenumber side of the centers decay much more rapidly than do Lorentz lines, by about the same amount as has been previously shown for the high wavenumber side. However, an asymmetrical correcting line shape factor is needed to obtain good agreement between experimental and synthetic spectra.

Collisionally induced population transfer effect in infrared absorption spectra. II. The wing of the Ar‐broadened ν3 band of CO2

The absorption beyond the ν3‐band head of CO2 broadened by argon has been measured at room temperature. The absorption exhibits a strong sub‐Lorentzian behavior (several orders of magnitude) resulting from collisionally induced line interferences which transfer intensity from this wing region to the ν3‐band center. This wing absorption region implies detuning frequencies from resonances much larger than the reciprocal duration of collision. Consequently, finite duration of collisions in rotational energy transfers and initial correlations must be included in absorption calculation. A line‐by‐line coupling theory accounting for both these effects has been recently proposed [J. Chem. Phys. 89, 625 (1988)] and is applied here to a detailed study of the CO2–Ar collisional system. A convenient generalized detailed balance correction is introduced in this theory to overcome the limitation of the assumed resonant character of the energy transfer in the short time limit with respect to the thermal time ( βℏ)−1. T...

Line mixing effects in the 0003–0000 band of CO2 in helium. III. Energy corrected sudden simultaneous fit of linewidths and near wing profile

Line coupling induced by collisions leads to drastic modifications of the spectral profile of the 0003–0000 of CO2 pressurized by helium. Calculation of these modifications have been performed by using two recent energy corrected sudden (ECS) formalisms. The two formulations lead to theoretical predictions rather similar and in good agreement with the available data over extended ranges of frequency and perturber pressure. It has been shown that a simultaneous fit of the pressure broadened linewidths and the near wing profile allows a more accurate determination of the basic ECS parameters. For that purpose, it has been necessary to extend the measurement of the broadened widths to high J values (up to J≊90).

Variable path-length, low-temperature cells for absorption spectroscopy

Design and performance affect various single and multiple pass, low-temperature absorption cells. These cells currently operate with path lengths from 10-3 up to 80 m and are used in the 119-300K temperature range and the 0-10 bars (0-1 MPa) pressure range.

Line mixing effects in the 00°3–00°0 band of CO2 in helium. II. Theoretical analysis

In paper I of this series, important deviations from an additive superposition of Lorentzian profiles were experimentally evidenced in the 00°3–00°0 band of CO2 in He. All the observed deviations are explained by the collision‐induced line mixing effects which schematically transfer intensity from the wing of the band to its central part. The IOS approximation has been found to be insufficient while, the ECS approximation leads to theoretical predictions in good agreement with the experimental data over extended ranges of frequency and perturber pressure. However it must be emphasized that it has been necessary to resort to the method in current use for the determination of the fundamental rates, an ad hoc adjustement starting from the observed linewidths.

Line shape in the low frequency wing of self- and N 2 -broadened ν 3 CO 2 lines: temperature dependence of the asymmetry

The shape of the far wing of self- and N(2)-broadened CO(2) lines has been investigated in the 2150-2250-cm(-1) spectral region, i.e., on the low wavenumber side of the lines of the very intense v(3) band of (12)C(16)O(2) in a temperature range of atmospheric interest (200-300 K). The experimental results have been compared to calculated values based on the AFGL 1986 compilation. It appears that a symmetrical sub-Lorentzian line shape based on experiments made on the high wavenumber side cannot reproduce experiments. Comparison with experiments made at room temperature shows that the asymmetry of the correcting line shape factor chi strongly increases when decreasing the temperature.

Carbon furnace infrared source

A carbon furnace which is a useful source, for high resolution spectroscopy has been built. It offers several advantages over previous furnaces. Higher temperatures are reached, and no significant temperature gradient is present upon the rod. High stability temperature and a long life of the rod are offered.

Line mixing effects in the 00°3–00°0 band of CO2 in helium. I. Experiment

The shape of the 00°3–00°0 CO2 band in helium has been investigated at room temperature over an extended range of perturber pressures (0–140 atm). Various and strong deviations from an additive superposition of Lorentzian lines have been observed, due to important line mixing effects enhanced by the specific structure of the R branch in this band.

Réalisation d’un spectromètre infra-rouge de résolution moyenne, corrigé de la coma

A middle resolution spectrometer according to a symmetrical Z-shaped setup in a vertical plane is described. The arrangement with the slits over and under the grating reduces coma and eliminates unwanted reflections.

Line shape in the low-frequency wing of N 2 and O 2 broadened CO 2 lines

The shape of the far wings of N(2) and O(2) broadened CO(2) lines have been investigated, at room temperature, in the 2140-2250-cm(-1) spectral region, i.e., on the low wavenumber side of the lines of the most intense band (nu(3) of (12)C(16)O(2)). The experimental results have been compared with calculated values based on the AFGL 1982 compilation. From this comparison it appears that the wings of the lines on the low wavenumber side of the centers decay much more rapidly than do Lorentz lines, by about the same amount as has been previously shown for the high wavenumber side. However, an asymmetrical correcting line shape factor is needed to obtain good agreement between experimental and synthetic spectra for wavenumbers sigma less, similar 2190 cm(-1).