Observation of the electronic band system 2³s_g^--a³p_u of C₂ in the vacuum ultraviolet region

A systematic spectroscopic study of the dicarbon molecule C-2 has important applications in various research fields, such as astrochemistry and combustion. In the short vacuum ultraviolet (VUV) wavelength region, recent theoretical calculations have predicted many absorption band systems of C-2, but only few of them have been verified experimentally yet. In this work, we employed a tunable VUV laser radiation source based on the two-photon resonance-enhanced four-wave mixing method and a time-of-flight mass spectrometer to investigate the absorption bands of C-2 in the VUV range of 64 000-66 000 cm(-1). The electronic transition 2(3)s(g)(-)(v')-a(3)p(u)(v') of C-2 has been observed and identified experimentally for the first time. The term value T-e for the 2(3)s(g)(-) state is determined to be 66 389.9 +/- 0.5 cm(-1) above the ground state X(1)s(g)(+), and the vibrational and rotational constants are also determined. The experimentally measured spectroscopic parameters in this study are in excellent agreement with the theoretical results based on high-level ab initio calculations.