Showing papers by "Guy Millot published in 1991"

Collisional broadening, line shifting, and line mixing in the stimulated Raman 2ν2 Q branch of CH4

Abstract: Self‐, argon‐, and helium‐broadening coefficients have been measured for 13 lines in the 2ν2 Raman Q branch of CH4 using stimulated inverse Raman spectroscopy. The linewidths clearly show the symmetry‐state dependence characteristic of pressure broadening, and inelastic processes in general, involving spherical‐top molecules. Pressure‐induced line shifts have also been measured for these features in pure methane. The pressure‐shift coefficients do not display the symmetry‐state dependence found for the linewidths. By applying the Rosenkranz perturbation treatment to a pair of collisionally mixed lines, we have been able to obtain an estimate of individual state‐to‐state contributions to the overall linewidth.

Rotational relaxation of nitrogen in ternary mixtures N2–CO2–H2O: Consequences in coherent anti‐Stokes Raman spectroscopy thermometry

Abstract: The influence of CO2 and H2O on the rotational relaxation processes of N2 in ternary mixtures N2–CO2–H2O is investigated. The efficiency of these perturbers is responsible for significant modifications of the state‐to‐state relaxation rates and broadening coefficients. Flame data are well reproduced by taking into account these modifications. The role of these minor species in the determination of temperatures in premixed flames is analyzed. The present relaxation model allows us to understand why the discrepancy between observed and calculated coherent anti‐Stokes Raman spectroscopy (CARS) spectra in flames is sometimes resolved by empirically adding a dephasing component to pure nitrogen linewidths. Moreover, this model improves the accuracy of CARS temperature measurements.