Measurements of the Rovibrationally Dependent Lifetimes of C₂ in the 1³Σ_g⁺ and <i>f</i>³Σ_g^– States through the VUV-Pump–UV-Probe Scheme

The dicarbon molecule, C₂, is one of the most important diatomic species in various gaseous environments. Despite extensive spectroscopic studies in the last two centuries, the radiative and photodissociative properties of C₂ in its highly excited electronic states are still largely unexplored, particularly in the short vacuum ultraviolet (VUV) region. In this study, the lifetimes of C₂ for rotational levels in the recently identified 1³Σ_g⁺ state up to the vibrational level ν' = 4 and in the <i>f</i>³Σ_g^- state up to ν' = 2 are measured for the first time with a VUV-pump-UV-probe photoionization scheme. It is found that all rovibrational levels in the <i>f</i>³Σ_g^- state have lifetimes shorter than the dynamical limit of ∼4.7 ns of the present method, and the lifetimes in the 1³Σ_g⁺ state show obvious and complex dependence on the rotational and vibrational quantum levels. Generally, the lifetime in the 1³Σ_g⁺ state becomes shorter at higher rotational and vibrational levels, i.e., the longest lifetime measured in the ν' = 0 level is ∼18 ns, while all rotational levels in the ν' = 4 level are found to have shorter lifetimes than ∼4.7 ns. This implies that predissociation might occur and become more prominent at the higher energy levels in the 1³Σ_g⁺ state. The prominent dependence of the lifetime on the rotational, vibrational and electronic level indicates complex dynamical processes in the highly excited states of C₂.