  The ratio of deuterium to hydrogen (D/H ratio) of Solar System bodies is an
important clue to their formation histories. Here we fit a Neptunian
atmospheric model to Gemini Near Infrared Spectrograph (GNIRS) high spectral
resolution observations and determine the D/H ratio in methane absorption in
the infrared H-band ($\sim$ 1.6 {\mu}m). The model was derived using our
radiative transfer software VSTAR (Versatile Software for the Transfer of
Atmospheric Radiation) and atmospheric fitting software ATMOF (ATMOspheric
Fitting). The methane line list used for this work has only become available in
the last few years, enabling a refinement of earlier estimates. We identify a
bright region on the planetary disc and find it to correspond to an optically
thick lower cloud. Our preliminary determination of CH$_{\rm 3}$D/CH$_{\rm 4}$
is 3.0$\times10^{-4}$, which is in line with the recent determination of Irwin
et al. (2014) of 3.0$^{+1.0}_{-0.9}\sim\times10^{-4}$, made using the same
model parameters and line list but different observational data. This supports
evidence that the proto-solar ice D/H ratio of Neptune is much less than that
of the comets, and suggests Neptune formed inside its present orbit.
