  We report on the initial analysis of a Herschel/PACS full range spectrum of
Neptune, covering the 51-220 micrometer range with a mean resolving power of ~
3000, and complemented by a dedicated observation of CH4 at 120 micrometers.
Numerous spectral features due to HD (R(0) and R(1)), H2O, CH4, and CO are
present, but so far no new species have been found. Our results indicate that
(i) Neptune's mean thermal profile is warmer by ~ 3 K than inferred from the
Voyager radio-occultation; (ii) the D/H mixing ratio is (4.5+/-1) X 10**-5,
confirming the enrichment of Neptune in deuterium over the protosolar value (~
2.1 X 10**-5); (iii) the CH4 mixing ratio in the mid stratosphere is
(1.5+/-0.2) X 10**-3, and CH4 appears to decrease in the lower stratosphere at
a rate consistent with local saturation, in agreement with the scenario of CH4
stratospheric injection from Neptune's warm south polar region; (iv) the H2O
stratospheric column is (2.1+/-0.5) X 10**14 cm-2 but its vertical distribution
is still to be determined, so the H2O external flux remains uncertain by over
an order of magnitude; and (v) the CO stratospheric abundance is about twice
the tropospheric value, confirming the dual origin of CO suspected from
ground-based millimeter/submillimeter observations.
