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P. N. Mohammed, P. G. Steffes (Georgia Institute of Technology)
A model, based on the Van Vleck-Weisskopf lineshape, was developed for the centimeter-wavelength opacity of PH3, which provides an order of magnitude improvement over previous models (Hoffman et al. ICARUS 152, 172-184, 2001). This formalism utilizes line intensities from the JPL (Pickett et al. 1998) catalog which have been selectively weighted to fit the centimeter wavelength laboratory data. The collisionally induced rotational lines which are lower in frequency than the first rotational line of J = 1 to 0 (267 GHz) have not been measured directly, thus in order to fit the data, weightings were given to those lines below 40 GHz. New laboratory measurements are currently being conducted to investigate whether this model is also accurate at 94 GHz (3.2 mm) under conditions for the outer planets. Preliminary measurements at room temperature agree well with this centimeter-wave formalism for PH3 opacity suggesting that the intensities of only the first 40 lines of the JPL catalog need to be weighted. Further measurements of the opacity and refractivity of PH3 in a hydrogen/helium (H2/He) atmosphere are being conducted at 94 GHz (3.2 mm) at pressures of 0.5, 1 and 2 bars and at temperatures of 210 K and 193 K. Additionally, new high-precision laboratory measurements of the opacity and refractivity of NH3 in an H2/He atmosphere will be conducted under the same frequency, temperature and pressure conditions described for PH3. These new measurements will better constrain the NH3 opacity model for use over a broader wavelength range. Results of measurements of both PH3 and NH3 can be used to better interpret maps of Saturn’s emission at this wavelength and can potentially deduce spatial variations in the abundances of both gases in the atmosphere of Saturn.
This work is supported by the NASA Planetary Atmospheres Program under grant NAG5-12122.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.