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

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 investi gated by high resolution stimulated Raman spectroscopy for various concentr ations and temperatures. A model, successfully used for binary mixtures, is extended to ternary mixtures. An excellent agreement is obtained between t heory and experiment for H-2-Ar-N-2, by using the collisional parameters pr eviously 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 echanism for H-2-Ar or H-2-N-2. The present experimental results allow us, via the frame of our model, to determine the "hardness" parameter values fo r H-2-He (inaccessible from binary mixtures data) and to get an accurate de scription of the spectral line shape. This study should be useful for hydro gen coherent anti-Stokes Raman spectroscopy thermometry in H-2/air flames a t high pressure through its possible extension to the H-2-N-2-H2O system. ( C) 2000 American Institute of Physics. [S0021- 9606(00)00346-9].