A New Band System of the Dicarbon Molecule in the Vacuum Ultraviolet Region.

Abstract

As one of the most abundant molecules in the universe, the long history of spectroscopic studies of the dicarbon molecule, C2, reaches back two centuries. While many electronic band systems with upper states below the lowest dissociation threshold have been well characterized, much less is known about transitions to higher-lying states. Here, we report the observation of a new band system of C2 from the lowest triplet state a3Πu through a resonance-enhanced multiphoton ionization scheme. The upper state is identified as 13Σg+, which is determined to be 61539.0 cm-1 (7.630 eV) above ground state X1Σg+. The spectroscopic parameters determined for the 13Σg+ state are in excellent agreement with those predicted by the high-level ab initio calculations. This study paves the way for systematic investigations of the photoabsorption and photodissociation of C2 in the vacuum ultraviolet region, which has important applications in the field of astrochemistry.