Electronic Absorption Spectra of H2C6O+ Isomers : Produced by Ion-Molecule Reactions

Three absorption systems with origin at 354, 497 and 528 nm were detected after mass-selected deposition of H2C6O+ in a 6 K neon matrix. The ions were formed by the reaction of C2O with HC4H+ in a mixture of C3O2 and diacetylene in a hot cathode source, or by dissociative ionization of tetrabromocyclohexadienone. The 497 and 354 nm systems are assigned to the 1 2A'' ← X 2A'' and 2 2A'' ← X 2A'' electronic transition of B+, (2-ethynylcycloallyl)methanone cation and the 528 nm absorption to 1 2A2 ← X 2B1 of F+, 2-ethynylbut-3-yn-1-enone-1-ylide, on the basis of calculated excitation energies with CASPT2.