The formation of fluorescent and metastable fragments by photoexcitation of some diatomic molecules in the vacuum ultraviolet region

The formation of fluorescent and metastable fragments from four diatomic molecules, i.e. O₂, N₂, NO and CO, has been investigated in the vacuum ultraviolet region. The neutral particles are detected by using a microchannel plate stack, where retarding electric potentials prevent charged particles from reaching the detector. Every diatomic molecule investigated here shows the formation of fluorescent and metastable fragments in particular photon energy regions. Three Rydberg states of O₂ converging to O₂⁺(a ⁴Π_u) undergo both neutral dissociation processes forming fluorescent [O⁺(⁴S)]3s ³S₁ and metastable [O⁺(⁴S)]3s ⁵S₂; the yield curve for each fragment is determined. Direct and cascade formation of the fluorescent [N⁺(³P)]3s ⁴P fragment from N₂ are separated, and it is found that the dissociation of the 4sσ Rydberg state converging to N₂⁺(C ²Σ_u⁺) preferentially produces [N⁺(³P)]3p fragments, but not or weakly the [N⁺(³P)]3s ⁴P fragment. High-n Rydberg states converging to NO⁺(c ³Π) and CO⁺(D ²Π) undergo neutral dissociation described by the core ion model, resulting in large peaks for neutral particle formation.