Infrared spectroscopic and theoretical study of the HC(2n+1)O(+) (n = 2-5) cations.

The carbon chain cations, HC(2n+1)O(+) (n = 2-5), are produced via pulsed laser vaporization of a graphite target in supersonic expansions containing carbon monoxide and hydrogen. The infrared spectra are measured via mass-selected infrared photodissociation spectroscopy of the CO "tagged" [HC(2n+1)O·CO](+) cation complexes in the 1600-3500 cm(-1) region. The geometries and electronic ground states of these cation complexes are determined by their infrared spectra compared to the predications of theoretical calculations. All of the HC(2n+1)O(+) (n = 2-5) core cations are characterized to be linear carbon chain derivatives terminated by hydrogen and oxygen, which have the closed-shell singlet ground states with polyyne-like carbon chain structures.