BROAD-BAND SUBMILLIMETER SPECTROSCOPY OF HCN, NH3, AND PH3, IN THE TROPOSPHERE OF JUPITER

We report measurements of the Jupiter brightness spectrum in the 850-m u m and 1100-mu m atmospheric windows with a spectral resolution of 12 5 MHz, obtained with a Fourier transform spectrometer on the James Cle rk Maxwell Telescope. Three results were obtained, First, the predicte d absorption features due to the rotational lines of HCN at 266 and 35 4 GHz were not detected within our error limits of less than 1%. We es tablish new upper limits for the HCN abundance in the jovian troposphe re for five assumed abundance distributions and for two assumed NH, ab undances, The upper limits are 1.7 to 13 times smaller than the abunda nce value obtained in the only reported detection of HCN in Jupiter pr ior to the impact of Shoemaker-Levy 9, Second, the continuum brightnes s temperature spectrum at 850 mu m was determined and is in agreement with previous measurements, but has large error bars due to uncertaint ies in the photometric calibration. We estimate the ammonia abundance in the 1-2 bar region to be 1.7 times solar, but this result is tentat ive since scattering by NH3 cloud particles and absorption by gaseous H2S were neglected in our atmospheric model. Finally, the first rotati onal line of PH3 at 267 GHz was not detected, a result which we demons trate is consistent with the statistical noise level in these measurem ents, with current values of the spectroscopic parameters, and with ph osphine measurements at other wavelengths. (C) 1997 Academic Press.