DETECTION OF THE 267 GHZ J=1-0 ROTATIONAL TRANSITION OF PH3 IN SATURNWITH A NEW FOURIER-TRANSFORM SPECTROMETER

In recent observations with a Fourier transform spectrometer at the Ca ltech Submillimeter Observatory, we have detected the highly pressure- broadened (FWHM = 11.2 GHz) J = 1-0 rotational transition of PH3 (phos phine) on Saturn. By modeling the saturnian atmosphere with a radiativ e transfer code, we find that the observed line profile is consistent with a constant PH3 mole fraction of 3.0 +/- 1.0 ppm in the upper trop osphere. A best fit to the depth of the line implies a cutoff at high altitudes, with no PH3 present at pressures less than or similar to 10 0 mbar. The observed line depth, combined with the lack of a detectabl e emission core, implies that a cutoff in the PH3 abundance occurs at a pressure between 13 and 140 mbar. We did not detect PH3 in Jupiter o r any other molecular lines between 195 and 295 GHz (1.54 mm and 1.02 mm, respectively) in either Jupiter or Saturn. (C) 1994 Academic Press , Inc.