The pressure broadening and shifting, of the S0(J = 0–4) pure rotational Raman lines of normal hydrogen, have been determined from 1 to 35 amagat units of density, at 29.8 °C. Over the range of densities explored, the width and shift of the lines are linear functions of the density. Our precise results may be reconciled with earlier measurements at higher densities by adding a term cubic in the density for the widths and quadratic in the density for the shifts. It is argued that the present results are safely within the impact regime and may be compared with calculations when they become available. The accuracy obtained is about 0.2 MHz per amagat [Formula: see text], for the broadening, and ranges from 0.1 to 0.3 MHz per amagat [Formula: see text] for the shifting coefficients. An analysis of the results indicate that it may be possible to combine the shifts of the pure vibrational and the pure rotational Raman lines to disentangle the contributions of the isotropic and anisotropic intermolecular forces to the perturbation of molecular spectra. Departures from linear broadening and shifting, at high density, are discussed.

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Precise spectral line measurements of carbon monoxide in an operating pressure modulator cell permit independent determinations of the instantaneous gas temperature and pressure.