Infrared Photodissociation Spectroscopic and Theoretical Study of the HC2n O+ (n=3-6) Cations

The carbon chain cations, HC2n O+ (n=3-6) are produced via a pulsed laser vaporization supersonic expansion ion source in the gas phase. Their infrared spectra are measured via mass-selected infrared photodissociation spectroscopy of the CO "tagged" [HC2n O center dot CO](+) cation complexes in 1600-3500 cm(-1) frequency range. The geometric and electronic structures of the [HC2nO center dot CO](+) complexes and the core HC2n O+ (n=3-6) cations are determined with the aid of density functional theory calculations. These HC2n O+ (n=3-6) ions are identified to be linear carbon chain derivatives terminally capped by hydrogen and oxygen. The triplet ground states are 10-15 kcal/mol lower in energy than the singlet states, indicating cumulene-like carbon chain structures.