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

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…

Femtosecond time resolved coherent anti-Stokes Raman spectroscopy: Experiment and modelization of speed memory effects on H2-N2 mixtures in the collision regime

194317; With the aim of temperature diagnostic, femtosecond time-resolved CARS (coherent anti-Stokes Raman spectroscopy) is applied to probe H2 in H2-N2 mixtures. In a first part, a Lorentzian profile is used to model the femtosecond CARS response. A difference between the experimental broadening and the expected one is observed in the collision regime. The observed broadening increases strongly in an inhomogeneous way with respect to the perturber concentration. This is of considerable importance for temperature measurements. In a second part, we show that in the collision regime, this inhomogeneous broadening is due to the speed dependence of the collisional parameters and the memory effe…

H-2 vibrational spectral signatures in binary and ternary mixtures: theoretical model, simulation and application to CARS thermometry in high pressure flames

International audience; A summary of the main results obtained by the two groups in the field of H-2 vibrational spectral line signatures for various mixtures. in connection with CARS diagnostics of H-2-O-2 combustion systems, is presented. H-2-X Systems may have specific large inhomogeneous spectral features, due to the dependence of the line broadening and line shifting on the (H-2) radiator speed, particularly at high temperature. Thus, careful attention has to be paid to rigorously analyze such features, both from the experimental point of view (Dijon) and from the theoretical one (Besancon). Applications of the present results to high-pressure H-2/air flame thermometry are also briefly…

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

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…

Temperature measurement in gas mixtures by femtosecond Raman-induced polarization spectroscopy

The potential of femtosecond Raman-induced polarization spectroscopy (RIPS) for the simultaneous determination of temperature and concentrations was investigated. These measurements were related to the rotational time response of the molecular gas mixture, which was measured as a function of the pump-probe time delay. The change of the polarizability anisotropy with respect to the vibrational levels was taken into account. The results of temperature measurements in pure CO2 showed good agreement with the values obtained by a thermocouple. The RIPS technique was also applied to a CO2-N2 gas mixture to determine simultaneously temperatures and concentrations at temperatures up to 600 K. The a…

Spectroscopie Raman Anti-Stokes Cohérente femtoseconde (DRASC – fs) : expériences et modélisation dans le cas du mélange H2 – N2 à basse pression

Dans l'objectif du diagnostic de la temperature dans les milieux en combustion, la Diffusion Raman Anti-Stokes Coherente resolue en temps (DRASC - fs) est utilisee pour sonder H 2 dans les melanges H 2 -N 2 a basse pression. Le dispositif DRASC mis en place est decrit en detail. Un nouveau modele de la reponse DRASC temporelle, prenant en compte tous les effets collisionnels specifiques a l'hydrogene (effets dits « de vitesse ») est presentee, ainsi que la comparaison avec l'experience, l'accord se revelant tres satisfaisant.

Speed-memory effects in H2-N2 mixtures studied by CARS femtosecond. Experiments and modelization from the collisional to the Doppler regime

Femtosecond Raman time-resolved molecular spectroscopy

International audience; The applicability of several femtosecond time resolved non-linear coherent techniques such as Raman induced polarization spectroscopy (RIPS), degenerate four-wave mixing (DFWM) and coherent anti-Stokes Raman spectroscopy (CARS) for molecular spectroscopy is presented. All methods rely on the initial coherent excitation of molecular states producing wavepackets, whose time evolution is then measured. In the case of RIPS and DFWM only pure rotational transitions are involved, whereas in CARS vibrational states can be excited. First the methodology of concentration and temperature measurements using RIPS in gas mixtures involving N2, CO2, O2, and N2O is shown. In additi…

Femtosecond Raman time-resolved molecular spectroscopy

Abstract The applicability of several femtosecond time resolved non-linear coherent techniques such as Raman induced polarization spectroscopy (RIPS), degenerate four-wave mixing (DFWM) and coherent anti-Stokes Raman spectroscopy (CARS) for molecular spectroscopy is presented. All methods rely on the initial coherent excitation of molecular states producing wavepackets, whose time evolution is then measured. In the case of RIPS and DFWM only pure rotational transitions are involved, whereas in CARS vibrational states can be excited. First the methodology of concentration and temperature measurements using RIPS in gas mixtures involving N2, CO2, O2, and N2O is shown. In addition some applica…

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

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…

Speed-dependent line profile: A test of a unified model from the Doppler to the collisional regime for molecule-molecule collisions

International audience; A speed-dependent line profile combining soft and hard fully correlated Dicke-narrowing collisions was recently successfully tested on Ar-broadened H-2 spectra in a wide density and temperature range. A further test for mixtures of H-2 in nitrogen molecules (instead of Ar atoms) is presented. This test is also based on high resolution Raman investigation of the isotropic Q(1) line of H-2 from low to high density at various temperatures. The same consistency of the speed-dependent line profile as for H-2-Ar is obtained for H-2-N-2 through a remarkable agreement with all the data by using a unique set of four parameters (the collisional width and shift, the kinetic fre…