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

In recent observations with a Fourier transform spectrometer at the Caltech Submillimeter Observatory, we have detected the highly pressure-broadened (FWHM = 11.2 GHz) J = 1-0 rotational transition of PH3 (phosphine) on Saturn. By modeling the saturnian atmosphere with a radiative 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 troposphere. 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 100 mbar. The observed line depth, combined with the lack of a detectable 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 or 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.