  Studying chemistry and chemical composition is fundamental to go back to
formation history of planetary systems. We propose here to have another look at
five targets to better determine their composition and the chemical mechanisms
that take place in their atmospheres. We present a re-analysis of five Hot
Jupiters, combining multiple instruments and using Bayesian retrieval methods.
We compare different combinations of molecules present in the simulated
atmosphere, different chemistry types as well as different clouds
parametrization. As a consequence of recent studies questioning the detection
of Na and K in the atmosphere of HD 209458b as being potentially contaminated
by stellar lines when present, we study the impact on other retrieval
parameters of misinterpreting the presence of these alkali species. We use
spatially scanned observations from the grisms G102 and G141 of the WFC3 on
HST, with a wavelength coverage of $\sim$0.8 to $\sim$1.7 microns. We analyse
these data with the publicly available Iraclis pipeline. We added to our
datasets STIS observations to increase our wavelength coverage from $\sim$0.4
to $\sim$1.7 microns. We then performed a Bayesian retrieval analysis with the
open-source TauREx using a nested sampling algorithm. We explore the influence
of including Na and K on the retrieval of the molecules from the atmosphere.
Our data re-analysis and Bayesian retrieval are consistent with previous
studies but we find small differences in the retrieved parameters. After all,
Na and K has no significant impact on the properties of the planet atmospheres.
Therefore, we present here our new best-fit models, taking into account
molecular abundances varying freely and equilibrium chemistry. This work is a
preparation for a future addition of more sophisticated representation of
chemistry taking into account disequilibrium effects such as vertical mixing
and photochemistry.
