Experimental lifetime measurements of C2 in the high-lying (2−4)3Δg states

The dicarbon (C2) molecule is an important molecu-lar species observed in many carbon-containing gaseous environments. The spectroscopic and dissociative studies of C2 have attracted great attention for a long time for understanding its electronic characters as well as the evolution and cycling of carbon in the universe. In this study, the lifetimes of C2 populated at the three high-lying electronic states of (2−4)3Δg in the vacuum ultraviolet (VUV) region have been experimentally measured using a time-of-flight mass spectrometer and the VUV-pump−UV-probe photoionization scheme. The measurements showed that all the rovibronic levels in the 2(g)3Δg state exhibit shorter lifetimes than the dynamical limit of the experimental method, consistent with the theoretically predicted radiative lifetimes. Dependence of the lifetime on the vibrational level was observed in the 33Δg state, and a marginal rotational dependence was noticed in the v′=1 vibrational level. For the 43Δg state, the rotationally resolved lifetimes in the vʹ=1 vibrational level were found to be slightly longer than those in the v′=0 and 2 vibrational levels. Such a complicated dependence of the lifetime on the rovibronic level makes further experimental and theoretical investigations highly desired for understanding the dynamics in the high-lying excited states of C2.