The B ¹B₁ State of Cyclopropenylidene, c-C₃H₂

The B 1 B 1 ← X 1 A 1 transition of isolated cyclopropenylidene, c -C 3 H 2, has been studied by multiphoton ionization and H-atom photofragment Doppler spectroscopy. The carbene is produced by flash pyrolysis of 1-chlorocycloprop-2-ene. Three bands are observed at 271.0, 266.9, and 264.6 nm. The 271 nm band is assumed to be the origin of the transition, in agreement with TD-DFT computations that yield a vertical excitation energy of 4.74 eV (262 nm). The appearance of H-atom photofragments indicates that c -C 3 H + H is an important reaction channel at UV excitation energies.