CO energy potential curves on the left and a schematic of the UV fluorescence mechanism on the right. We are concerned with transitions between the ground electronic state X¹Σ⁺ and the electronic excited state A¹Π. The arrows show a possible UV-fluorescence pumping from a ground electronic level (X¹Σ⁺) at v′′ = 1 to a level in the electronic state A¹Π, followed by a de-excitation to the level v′′ = 2 in the ground electronic state. The value for the curves are taken from Cooper & Kirby (1987).