  The goal is to determine the composition of Pluto's atmosphere and to
constrain the nature of surface-atmosphere interactions.
  We perform high--resolution spectroscopic observations in the 2.33--2.36
$\mu$m range, using CRIRES at the VLT.
  We obtain (i) the first detection of gaseous methane in this spectral range,
through lines of the $\nu_3$ + $\nu_4$ and $\nu_1$ + $\nu_4$ bands (ii) strong
evidence (6-$\sigma$ confidence) for gaseous CO in Pluto. For an isothermal
atmosphere at 90 K, the CH$_4$ and CO column densities are 0.75 and 0.07 cm-am,
within factors of 2 and 3, respectively. Using a physically--based thermal
structure model of Pluto's atmosphere also satisfying constraints from stellar
occultations, we infer CH$_4$ and CO mixing ratios q$_{CH_4}$=
0.6$^{+0.6}_{-0.3}$% (consistent with results from the 1.66 $\mu$m range) and
q$_{CO}$ = 0.5$^{+1}_{-0.25}$$\times10^{-3}$. The CO atmospheric abundance is
consistent with its surface abundance. As for Triton, it is probably controlled
by a thin, CO-rich, detailed balancing layer resulting from seasonal transport
and/or atmospheric escape.
