ISO OBSERVATIONS OF URANUS - THE STRATOSPHERIC DISTRIBUTION OF C2H2 AND THE EDDY DIFFUSION-COEFFICIENT

The infrared spectrum of Uranus has been recorded between 7 and 16.5 m u m with the grating mode of the Short-Wavelength Spectrometer of ISO, with a resolving power of 1500. The 6-12 mu m spectrum of Uranus has also been recorded at lower resolution (R=90) by the PHOT instrument i n spectroscopic mode. The spectra show no signatures other than the C2 H2 band centered at 13.7 mu m. From the absence of emission in the reg ion of the CH4 7.7 mu m band, and by fitting the C2H2 data on the basi s of a photochemical model, the eddy diffusion coefficient is retrieve d (in the range 5 10(3)-10(4) cm(2) s(-1) at the homopause). This resu lt is consistent with the values previously derived from the Voyager U V occultation experiments.