High-resolution infrared spectra of Mercury (1.9-2.7 , resolution limit 0.134 cm -1) obtained with the original "Connes" interferometer at the Steward Observatory 90-inch telescope have provided a very sensitive test for the possible presence of a CO2, CO atmosphere. An improved upper limit of 0.12 cm-atm (1.0 x 10- mb surface pressure) has been set for CO2, and a new upper limit of 0.05 cm-atm (2.0 x 10-0 mb surface pressure) has been set for CO. Upper limits of similar magnitude can be established for CH4 and NH2. From the separation of the Mercury signal into reflected sunlight and thermal emission, we determine that the reflectivity decreases toward longer wavelengths and has a value of about 0.06 at 2.25 . Implications for the possible evolution of an atmosphere on Mercury are discussed. Subject headings: abundances, planetary - atmospheres, planetary - Mercury - spectra, infrared - spectra, planetary
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Fink et al. (1974) studied this question.