Infrared photodissociation spectroscopy of copper carbonyl cations

Copper carbonyl cations of the form Cu(CO)(n)(+) (n = 1-8) are produced in a molecular beam via laser vaporization in a pulsed nozzle source. Mass-selected infrared photodissociation spectroscopy in the carbonyl stretching region is used to study these ions and their argon "tagged" analogues. The geometries and electronic states of these complexes are determined by the number of infrared-active bands, their frequency positions, and their relative intensities compared to the predictions of theory. Cu(CO)(4)(+) has a completed coordination sphere, consistent with its expected 18-electron stability. It also has a tetrahedral structure similar to that of its neutral isoelectronic analog Ni(CO)(4). The carbonyl stretch in Cu(CO)(4)(+) (2198 cm(-1)) is blue-shifted with respect to the free CO vibration (2143 cm(-1)), providing evidence that this is a "non-classical" metal carbonyl.