Strongly Rotationally Dependent Lifetimes of C₂ in the 2³Σ_g^– State: Implications for Predissociation in the Vacuum Ultraviolet Region

The radiative and photodissociative properties of the dicarbon molecule, C₂, in high-lying electronic states are of utmost importance for modeling the photochemical processes that occur in various astronomical environments. Despite extensive spectroscopic studies in the last two centuries, the photodissociation properties of C₂ are still largely unknown, particularly for quantum states in the vacuum ultraviolet (VUV) region. Here, the lifetimes of C₂ for each individual rovibrational level in the recently identified 2³Σ_g^- state are measured for the first time using a VUV-pump-UV-probe photoionization scheme. The lifetimes are found to be strongly dependent on the rotational and vibrational quantum levels in the 2³Σ_g^- state. The strongly rotationally dependent lifetimes observed here indicate that the 2³Σ_g^- state may mainly undergo a predissociation process through couplings with nearby repulsive electronic states. The current observation could have important applications in modeling the interstellar medium and cometary comae.