  Our purpose is to release a chemical network, and the associated rate
coefficients, developed for the temperature and pressure range relevant to hot
Jupiters atmospheres. Using this network, we study the vertical atmospheric
composition of the two hot Jupiters (HD209458b, HD189733b) with a model that
includes photolyses and vertical mixing and we produce synthetic spectra. The
chemical scheme is derived from applied combustion models that have been
methodically validated over a range of temperatures and pressures typical of
the atmospheric layers influencing the observations of hot Jupiters. We compare
the predictions obtained from this scheme with equilibrium calculations, with
different schemes available in the literature that contain N-bearing species
and with previously published photochemical models. Compared to other chemical
schemes that were not subjected to the same systematic validation, we find
significant differences whenever non-equilibrium processes take place. The
deviations from the equilibrium, and thus the sensitivity to the network, are
more important for HD189733b, as we assume a cooler atmosphere than for
HD209458b. We found that the abundances of NH3 and HCN can vary by two orders
of magnitude depending on the network, demonstrating the importance of
comprehensive experimental validation. A spectral feature of NH3 at 10.5$\mu$m
is sensitive to these abundance variations and thus to the chemical scheme. Due
to the influence of the kinetics, we recommend the use of a validated scheme to
model the chemistry of exoplanet atmospheres. Our network is robust for
temperatures within 300-2500K and pressures from 10mbar up to a few hundreds of
bars, for species made of C,H,O,N. It is validated for species up to 2 carbon
atoms and for the main nitrogen species.
