Broadening and shifting coefficients of Raman isotropic Q(j)( j=0, 1, 2) lines for pure H-2: coupled states and semiclassical calculations. Comparison with experiments

Quantum coupled states (CS) and semiclassical Robert-Bonamy (RB) calculatio ns of pure Hz broadening and shifting coefficients of Q(j) rovibrational li nes have been performed using a simple atom-atom potential energy surface ( PES). The main interest is to test the validity of the semiclassical method versus the CS calculation. This is the first comparison of the two methods for a diatom-diatom system for which rotation-rotation (R-R) energy transf ers contribute to the broadening and shifting coefficients. Agreement betwe en the two methods is found acceptable on the total result, but is excellen t when resonant or quasi-resonant rotational energy transfer do not occur. Comparison with experiment confirms the empirical laws used to model the te mperature dependence of the broadening and shifting coefficients. It also p ermits us to analyze through the semiclassical model, the weakness and adva ntages of the atom-atom PES used. (C) 2000 Elsevier Science B.V. All rights reserved.