Accurate Foreign-Gas-Broadening Parameters of the 22-GHz H2O Line from Refraction Spectroscopy

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Abstract
A differential microwave refractometer has been found to be an excellent tool for accurate study of foreign-gas broadening of isolated spectral lines. Many experimental and analytic difficulties disappear when foreign gas is admitted at the maximum of a self-broadened dispersion pressure profile. The new principle has been applied to determine the broadening efficiencies for helium, argon, oxygen, hydrogen, nitrogen, acetylene, carbon dioxide, and acetonitrile on the rotational transition Jτ:5−1 → 6−5 of water vapor at 22 GHz. The gases chosen represent a wide range in effective collision cross sections, as well as the main atmospheric constituents.