Measurement of the density shift of the ${\mathrm{H}}_2$ Q(0–5) transitions from 295 to 1000 K

We report results of a high-resolution inverse Raman spectroscopy study of the dependence on temperature and rotational quantum number J of the Raman Q-branch self-density-shift coefficients of pure (natural) hydrogen. The population-correlated J dependence of these coefficients, previously established at lower temperatures as a ‘‘coupling shift,’’ is observed to persist, almost independent of temperature, up to 1000 K. The temperature dependence of the overall shift is found to disagree above 500 K with extrapolations of recent theoretical calculations.