Collisional effects on spectral line shape from the Doppler to the collisional regime: A rigorous test of a unified model

2000

International audience; The paper presents high resolution Raman investigations of the Q(1) line of H-2 in Ar mixture from low density (Doppler regime) to high density (collisional regime) analyzed with a unique line shape profile. Measurements are performed by stimulated Raman gain spectroscopy between 300 and 1000 K in a wide density range (from 0.2 to 11 amagat). All the observed spectral features are accurately described by a unified model recently proposed by two of the authors. This model accounts for a velocity-memory process, not restricted to the usual hard and soft limits. It also includes correlation between velocity- and phase-changing collisions. An exhaustive analysis of vario…

Collisional line broadening and line shifting in N2-CO2 mixture studied by inverse Raman spectroscopy

1990

Abstract Collisional effects in the Raman Q-branch of N 2 perturbed by CO 2 have been studied by high-resolution stimulated Raman spectroscopy. The Raman spectra recorded in the 0.3–1.0 atm and 295–1000 K pressure and temperature ranges are fitted with a theoretical profile taking into account line broadening, frequency shift and line mixing due to rotational energy transfers. The data at low density are used as basic data for the modeling of rotationally inelastic rates through sets of adjustable parameters. We have used in this study the two main models developed in the last decade and known as modified exponential gap (MEG) and energy corrected sudden (ECS) laws. Experimental spectra rec…

Inhomogeneous speed effects on H-2 vibrational line profiles in ternary mixtures

2000

International audience; A study of speed inhomogeneous broadening of the hydrogen vibrational line profiles in the collisional regime for ternary mixtures is reported. The Q(1) line of H-2 in H-2-Ar-N-2, H-2-He-Ar, and H-2-He-N-2 mixtures is investigated by high resolution stimulated Raman spectroscopy for various concentrations and temperatures. A model, successfully used for binary mixtures, is extended to ternary mixtures. An excellent agreement is obtained between theory and experiment for H-2-Ar-N-2, by using the collisional parameters previously obtained from binary mixtures study. For H-2-He-Ar and H-2-He-N-2, H-2-He collisions play a "hardening" effect in the H-2 soft speed memory m…

Measurement of vibrational line profiles inH2–rare-gas mixtures: Determination of the speed dependence of the line shift

1994

High-resolution inverse Raman experiments for ${\mathrm{H}}_{2}$ diluted in Ar have revealed unusual Q-line profile features at various concentrations which have been interpreted in terms of speed-changing collisions. A more general approach including both speed- and phase-changing collisions has led to an alternative interpretation of these features. In order to further analyze the role of these various collisional mechanisms, new experiments have been performed. Pure ${\mathrm{H}}_{2}$ and ${\mathrm{H}}_{2}$ perturbed by Ne, Ar, and Xe have been investigated at various temperatures between 295 and 800 K.

Line coupling in Anisotropic Raman Branches

1994

Direct connection between collisional Raman cross sections and state‐to‐state rotational ones permits, within the sudden approximation, to evidence drastic decouplings from isotropic to anisotropic lines. These decouplings are consistent with the results obtained by using the strong collision model. Convenient energy corrections to the sudden approximation are used for N2 to calculate the resulting effects on the isotropic and anisotropic Q‐branch profiles in a large density range (several hundred bars). The comparison of the calculations with experimental coherent anti‐Stokes Raman scattering (CARS) and stimulated Raman (SRS) spectra of nitrogen exhibits a good agreement. Such effects coul…

H2-He vibrational line-shape parameters: Measurement and semiclassical calculation

1995

High-resolution inverse Raman spectroscopy has been used to obtain the line shifting and line broadening coefficients of H{sub 2} perturbed by He. Measurements have been made for the {ital Q}-branch transitions ({ital J}=0{r_arrow}5) in a density range of 10 to 20 amagat and from 296 to 995 K. Up to 795 K we have directly deduced from the experimental broadening coefficients the inelastic rotational state-to-state and vibrational dephasing rates. At higher temperatures, owing to the larger number of channels of relaxation which occur, the results have been analyzed using a scaling law. The line shift and broadening coefficients exhibit a square root and a linear dependence on temperature, r…

Collisional broadening and shifting parameters of the RamanQbranch ofH2perturbed byN2determined from speed-dependent line profiles at high temperatur…

1996

The broadening and shifting of the {ital Q} branch of H{sub 2} diluted in N{sub 2} are studied at temperatures between 300 and 1200 K. (i) In order to account for the observed anomalies (asymmetric profiles and nonlinearity of the linewidth versus perturber concentration), the results are interpreted using a speed-dependent model in its general form. This model introduces the speed dependence of the shift and the broadening. In contrast with the previous H{sub 2}{endash}rare-gas studies, the high-temperature measurements prove the necessity to include speed-dependent broadening that was ignored in the previous studies. (ii) Concomitantly, we report as well pure H{sub 2} results including Ra…

Hydrogen CARS thermometry in H2-N2 mixtures at high pressure and medium temperatures: influence of linewidths models

2000

International audience; In order to improve the accuracy of H2 CARS thermometry, H2 Q-branch CARS spectra have been recorded for various H2-N2 mixtures in a high-pressure cell at different pressures and temperatures (up to 40 bar and 875 K). Due to the low spectral resolution of broadband CARS experiments, the relevant spectral lineshape factor is the linewidth ratio G(Q(3))/G(Q(1)), since Q(1) and Q(3) are the most intense lines of the Q-branch spectrum in this temperature range. For the first time, the speed-inhomogeneous effects are accounted for in the simulation of the CARS profiles. The evaluated temperatures are in good agreement with reference values obtained by thermocouples. The s…

A direct study of the vibrational bending effect in line mixing: The hot degenerate 1110 ← 0110 transition of CO2

1997

Abstract The study of the isotropiv Raman Q -branch of a hot band Π ← Π allows one to establish a direct connection between the vibration-rotation angular momentum coupling and the resulting spectra. Due to the l -doubling, the Q -branch is split into two subbranches characterized by either even or odd rotational quantum number j . The vibrational bending reduces the rotational transfer rates inside each of these subbranches by a factor of about two and induces an inter-subbranch coupling. The expected propensity rule towards conservation of the parity index for high rotational levels is well observed. Calculated spectra are in excellent agreement with CARS experiments for the v 1 + v 2 ← v…

Caractérisation des mortiers et des pierres du Vieux Château

2013

A Powerful Tool to Study Collisional Phenomena and for Combustion Applications - the High-Resolution Stimulated Raman-Spectroscopy

1987

0302-0738

Study of Collisional Effects on Band Shapes of the v1/2v2 Fermi Dyad in CO2 Gas with Stimulated Raman-Spectroscopy .2. Simultaneous Line Mixing and D…

1990

0021-9606

Rotationally Inelastic Rates for N2-N2 System from a Scaling Theoretical Analysis of the Stimulated Raman Q-Branch

1988

0021-9606

Collisional Raman Linewidths of Nitrogen at High-Temperature (1700-2400 K)

1995

0146-9592; New high-temperature measurements of collisional linewidths of the Roman Q branch of nitrogen have been performed at 1700-2400 K with stimulated Raman spectroscopy in a tungsten filament. We fitted these data together with previous data obtained in the 295-1500-K range to redetermine the parameters of the relaxation models used in coherent anti-Stokes Raman spectroscopy thermometry. The improvement in the accuracy of the temperature measurement has been checked. Semiclassical calculations of linewidths in the 1700-2400-K range agree with the experimental data and have been extended to even higher temperatures.