We propose to use the LWS in grating-only mode to measure the
  integrated intensities of the 112.1-um R(0) and 56.2-um (R1)
  rotational lines of HD in the atmospheres of Uranus and Neptune.
  The results will be complementary to the Central Programme
  observations of the same lines using the LWS F-P.

  The determination of the deuterium abundances in the atmospheres
  of the giant planets is vital to our understanding of the
  composition of the primordial solar nebula and the early
  evolution of the planets. Use of the ISO LWS to measure these
  HD lines allows the abundances to be derived in a very direct
  and model-independent way.