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Many parameters constraining the spectral appearance of exoplanets are stillpoorly understood. We therefore study the properties of irradiated exoplanetatmospheres over a wide parameter range including metallicity, C/O ratio andhost spectral type. We calculate a grid of 1-d radiative-convective atmospheresand emission spectra. We perform the calculations with our newPressure-Temperature Iterator and Spectral Emission Calculator for PlanetaryAtmospheres (PETIT) code, assuming chemical equilibrium. The atmosphericstructures and spectra are made available online. We find that atmospheres ofplanets with C/O ratios $\sim$ 1 and $T_{\rm eff}$ $\gtrsim$ 1500 K can exhibitinversions due to heating by the alkalis because the main coolants CH$_4$,H$_2$O and HCN are depleted. Therefore, temperature inversions possibly occurwithout the presence of additional absorbers like TiO and VO. At lowtemperatures we find that the pressure level of the photosphere stronglyinfluences whether the atmospheric opacity is dominated by either water (forlow C/O) or methane (for high C/O), or both (regardless of the C/O). For hot,carbon-rich objects this pressure level governs whether the atmosphere isdominated by methane or HCN. Further we find that host stars of late spectraltype lead to planetary atmospheres which have shallower, more isothermaltemperature profiles. In agreement with prior work we find that for planetswith $T_{\rm eff}$ $<$ 1750 K the transition between water or methane dominatedspectra occurs at C/O $\sim$ 0.7, instead of $\sim$ 1, because condensationpreferentially removes oxygen.

Model atmospheres of irradiated exoplanets: The influence of stellar parameters, metallicity, and the C/O ratio