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R.N. Nelson (GaSoU/NASA-GSFC), J.E. Allen, Jr. (NASA-GSFC)
Although ethane (C2H6) is a trace constituent in the atmospheres of the outer planets and Titan, it plays an important role in the photochemistry of these atmospheres and in controlling their thermal profiles. Condensation as a haze or aerosol is one mechanism by which C2H6 is sequestered in these systems. The first-order equilibrium and photochemical models developed to describe this process are dependent on accurate vapor pressures of atmospheric constituents, such as C2H6, over the appropriate range of atmospheric parameters, e.g., temperature and pressure. Using an apparatus specifically designed for the determination of low-temperature vapor pressures, we have measured the vapor pressure of this molecule over the temperature range from 73 to 85 K, corresponding to vapor pressures of 6x10-6 and 1x10-3 Torr, respectively. This extends the available experimental data for this molecule by over two orders of magnitude in pressure.