NONDETECTION OF HYDROGEN-CYANIDE ON JUPITER

High spectral resolution observations of Jupiter performed at the NASA /Infrared Telescope Facility near 13.5 mu m are presented, Two spectra l ranges including the R(7) and R(11) lines of the v(2) band of HCN we re observed at high signal-to-noise. No evidence for HCN absorption in excess of 2% of the continuum was found, in contrast to the report by Tokunaga et al. (1981, Icarus 48, 283-289). An upper limit on the tro pospheric HCN mixing ratio of 1 x 10(-9) was derived, assuming a unifo rm value up to the tropopause. When HCN condensation in the upper trop osphere is taken into account, only a looser upper limit around 1.2 x 10(-8) can be set on the deep mixing ratio. The lack of emission cores at the position of the HCN lines provides an upper limit of 2 x 10(-4 ) cm-amagat on the HCN column density in the stratosphere (correspondi ng to a maximum average mixing ratio of 8 x 10(-10) above condensation level). A critical reanalysis of Tokunaga et al.'s observations is fi nally presented, leading to the conclusion that the previously reporte d detection of HCN is questionable. (C) 1996 Academic Press, Inc.