INVESTIGATIONS OF PURE ROTATIONAL TRANSITIONS OF H-2 SELF-PERTURBED AND PERTURBED BY HE - I - MEASUREMENT, MODELING, AND QUANTUM CALCULATIONS

High resolution stimulated gain Raman spectroscopy is used to investig ate the collisional parameters of pure rotational S-0(j = 0-4) lines o f H-2 in pure H-2 and H-2-He mixture. Measurements are performed betwe en 300 and 1000 K in a density regime where the lines are essentially collisionally broadened (typically 10 amagat). For the first time, the se highly accurate measurements of the frequencies of pure rotational lines allow one to correct previously measured values that did not tak e into account the collisional frequency shift. For both collisional s ystems,the shifting coefficients exhibit a Linear behavior with the sq uare root of temperature, similar to the behavior already observed in the Q branch. The broadening coefficients. bf the S-0 branch increase nonlinearly with temperature contrary to; the Q branch. For the H-2-He system, both these new S-0(j) data and previously measured Q(j) data are analyzed using a modeling of the broadening coefficients in terms of elastic and inelastic contributions. These different contributions are analyzed as ri function of temperature and of he rotational quantu m number j. Preliminary quantum calculations are used to assess the va lidity of the model. Further calculations will be presented in paper I I. (C) 1998 American Institute of Physics.