IR Spectroscopy and Theory of Cu+(H2O)Ar2 and Cu+(D2O)Ar2 in the O-H (O-D) Stretching Region: Fundamentals and Combination Bands

Copper-water ion-molecule complexes with attached argon atoms, Cu+(H2O)Ar-2, are produced in a supersonic molecular beam by pulsed laser vaporization. These systems are mass-selected in a reflectron time-of-flight spectrometer and studied with infrared photodissociation spectroscopy. The vibrational spectra for these complexes are characteristic of many cation-water systems, exhibiting symmetric and asymmetric O-H stretch fundamentals, and weaker features at higher frequency that have been tentatively assigned to combination bands. Using isotopically substituted spectra and model potential calculations, we are able to assign the combination bands to a water torsional vibration (frustrated rotation) in combination with the asymmetric stretch fundamental. This combination band assignment is likely to apply to IR spectra of many cation-water complexes.