Comparative analysis of purely classical and semiclassical approaches to collision line broadening of polyatomic molecules: II. C2H2–He case

The comparison of the classical method of Gordon and the semiclassical formalism of Robert and Bonamy was started in part I of this series of papers, dealing with the acetylene molecule perturbed by a heavy atom (Ar). The case of a light buffer gas (He) is considered in the present study. On the basis of a high-quality ab initio interaction potential, as previously, the influence of the roto-translational coupling on the trajectory parameters and its role in the line broadening at various temperatures are studied within the classical method. In addition, the line width contributions coming from the elastic (reorientation and dephasing) and inelastic collisions are separately analysed in the framework of both theoretical approaches. All these points confirm the previously stated conclusion that the roto-translational interactions play a non-negligible role in the collisional line broadening mechanisms. Also, a particular study in the framework of the classical approach enables some supplementary conclusions about the role of the perturber mass.