Giant planets are crucial to understand the origins of planetary systems. They are the first planets to form and their primitive atmospheres give us constrains on the physical and chemical conditions of the primordial nebula in which they were formed.

JWST′s large aperture and wide wavelength coverage will enable it to collect the highest quality transit spectra observed so far. For extrasolar giant planet atmospheres we expect to measure and retrieve the abundance of the most abundant molecules, such as H2O, CO, and CH4. Other molecules, such as H2S and PH3, have been observed in Jupiter and Saturn but their chemistry and detectability in strongly irradiated planets is highly unknown. Are they important for the chemistry of irradiated atmospheres? Can JWST detect them? In this seminar I will talk about about characterization of exoplanets through detailed atmospheric models. I will show the relevance of disequilibrium chemistry and of different species in the interpretation of exoplanet atmospheres data and the effect of stellar irradiation in their atmospheres.