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J. P. Hoffman, P. G. Steffes (Georgia Institute of Technology)
It has been suggested that phosphine (PH3) may contribute significantly to the microwave emission spectrum of Neptune, and to the centimeter-wavelength opacity measured by the Voyager 2 spacecraft at Neptune (DeBoer and Steffes, Icarus 123,1996) and at Saturn. As a result, laboratory measurements of the microwave opacity of PH3 in an H2/He atmosphere have been conducted at frequencies (wavelengths) of 1.5 GHz (20 cm), 2.2 GHz (13.3 cm), 8.3 GHz (3.6 cm), 13.3 GHz (2.3 cm), 21.6 GHz (1.4 cm), and 27 GHz (1.1 cm) over a range of temperatures (175-298 K) and pressures (1-6 Bars). A measurement-based centimeter-wavelength opacity formalism for phosphine has been developed and provides an order of magnitude improvement over previous models. The resulting model is applied to the Voyager 2 radio science experiment measurements at Saturn and Neptune. Applications of this model will serve to elucidate interpretation of centimeter-wavelength observations from radio telescopes and spacecraft radio occultation measurements at the atmospheres of all four jovian planets, including Cassini-Saturn.
We thank the NASA Planetary Atmospheres Program for supporting this work under grant NAG5-4190.
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