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

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 (colli sional 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 feat ures are accurately described by a unified model recently proposed by two o f the authors. This model accounts for a velocity-memory process, not restr icted to the usual hard and soft limits. It also includes correlation betwe en velocity- and phase-changing collisions. An exhaustive analysis of vario us possible mechanisms on the line shape is achieved. These mechanisms are the Dicke narrowing, the radiator speed dependence of the collisional broad ening and shifting parameters, the collisionally induced speed-class exchan ge and the nonimpact effect. The present test shows the high consistency of the unified model, since it allows one to get a remarkable agreement with all the data by using a unique set of parameters. This model should be usef ul for optical diagnostics at moderate density, as required for combusting media or atmospheric work. (C) 2000 American Institute of Physics. [S0021- 9606(00)00401-3].