We report the analysis of thermal-infrared observations of Neptune's disk by experiments on the Spitzer and Herschel Space Telescopes. The Spitzer data were obtained by the IRS instrument at wavelengths between 5.2 and 21.5 microns at a spectral resolving power, R 70, and at wavelengths between 10 and 21.5 microns at R 600. The Herschel observations were made by the PACS instrument's integral field spectrometer between 51 and 220 microns at R 3000, within the framework of the Key Project, ``Water and Related Chemistry in the Solar System''. Our analysis is set in the context of lower-resolution spectra obtained by the ISO LWS and SWS spectrometers covering wavelengths between 28 and 185 microns and the Akari IRC spectrometer covering wavelengths between 5.8 and 13.3 microns at R 40, together with spatially resolved ground-based studies of thermal emission. Our results indicate that that global-mean tropospheric temperatures are lower than those derived from the Voyager radio-occultation experiment, and consistent with the ISO results. Preliminary results (Lellouch et al. 2010 Astron. & Astrophys. In press) indicate that the D/H ratio is 4.5±1.0 x 10-5, consistent with enrichment of deuterium over the protosolar value, and the stratospheric column of H2O is 2.1±0.5 x 1014 cm-2. The peak CH4 abundance in the stratosphere is orders of magnitude larger than if it were cold-trapped below the mean 54-Kelvin tropopause minimum temperature - but consistent with injection from Neptune's warmer south polar region. Good fits to a variety of other stratospheric emission features are obtained: CO, CH3, CO2, C2H2, C2H4, C2H6, C3H8, C4H2. It is also possible to obtain a better fit to a spectral region dominated by C2H6 emission by adding 50-100 ppt of C6H6.< Réduire