Investigations of pure rotational transitions of H2 self-perturbed and perturbed by He. I. Measurement, modeling, and quantum calculations

High resolution stimulated gain Raman spectroscopy is used to investigate the collisional parameters of pure rotational S0(j=0–4) lines of H2 in pure H2 and H2–He mixture. Measurements are performed between 300 and 1000 K in a density regime where the lines are essentially collisionally broadened (typically 10 amagat). For the first time, these highly accurate measurements of the frequencies of pure rotational lines allow one to correct previously measured values that did not take into account the collisional frequency shift. For both collisional systems, the shifting coefficients exhibit a linear behavior with the square root of temperature, similar to the behavior already observed in the Q branch. The broadening coefficients of the S0 branch increase nonlinearly with temperature contrary to the Q branch. For the H2–He system, both these new S0(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 diff...