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The carbon monoxide rovibrational emission from discs around Herbig Ae starsand T Tauri stars with strong ultraviolet emissions suggests that fluorescencepumping from the ground X1 Sigma+ to the electronic A1 Pi state of CO should betaken into account in disc models. We implemented a CO model molecule thatincludes up to 50 rotational levels within nine vibrational levels for theground and A excited states in the radiative photochemical code ProDiMo. Wetook CO collisions with hydrogen molecules, hydrogen atoms, helium, andelectrons into account. We estimated the missing collision rates using standardscaling laws and discussed their limitations. UV fluorescence and IR pumpingimpact on the population of ro-vibrational v > 1 levels. The v = 1 rotationallevels are populated at rotational temperatures between the radiationtemperature around 4.6 micron and the gas kinetic temperature. The UV pumpingefficiency increases with decreasing disc mass. The consequence is that thevibrational temperatures, which measure the relative populations between thevibrational levels, are higher than the disc gas kinetic temperatures(suprathermal population). Rotational temperatures from fundamental transitionsderived using optically thick 12CO lines do not reflect the gas kinetictemperature. CO pure rotational levels with energies lower than 1000 K arepopulated in LTE but are sensitive to a number of vibrational levels includedin the model. The 12CO pure rotational lines are highly optically thick fortransition from levels up to Eupper=2000 K. (abridged)

Radiation thermo-chemical models of protoplanetary discs. IV Modelling CO ro-vibrational emission from Herbig Ae discs