This proposal is to use the Short Wavelength Spectrometer to detect
 the forbidden pure rotational spectrum of the H3+ molecular ion in the
 ionosphere of Jupiter. A detection of three or more lines, will:
 1) Be the first ever detection of this fundamental spectrum;
 2) Answer important questions about the concentration of H3+ in the
 jovian aurorae, and the physical conditions which prevail there.
 The H3+ ground state rotational spectrum covers the 10-40 micron
 region which is difficult to observe from the ground, but which is
 readily accessible to ISO's SWS. proposed to use the SWS in
 Fabry-Perot line scanning mode, to carry out the accurate measurements
 necessary to identify this spectrum. Several lines are need to compute
 the relevant temperature and column density.