The protonated water dimer is a prototypical system for the study of proton transfer in aqueous solution. We report infrared photodissociation spectra of cooled H+(H2O)2 [and D+(D2O2] ions, measured between 620 and 1900 wave numbers (cm-1). The experiment directly probes the shared proton region of the potential energy surface and reveals three strong bands below 1600 cm-1 and one at 1740 cm-1 (for H5O2+). From a comparison to multidimensional quantum calculations, the three lower energy bands were assigned to stretching and bending fundamentals involving the O...H+...O moiety, and the highest energy band was assigned to a terminal water bend. These results highlight the importance of intermode coupling in shared proton systems.

The gas-phase infrared spectroscopy of V 4 O 10 + produced by laser vaporization has been studied in the spectral region from 7 to 16 mm. Mass-selected V 4 O 10 + cations were stored in a helium filled radio frequency hexadecapole ion trap and excited using tunable infrared radiation from a free electron laser. The photodissociation spectrum was recorded by monitoring the V 4 O 8 + yield (O 2 loss) as a function of the excitation wavelength. Two absorption bands at 842 and 1032 cm À1 are observed, which are assigned to resonant excitation of the antisymmetric V-O-V stretching and V=O stretching vibrations, respectively. Comparison to recent theoretical and experimental studies indicate that the absorbing species consists of a V 4 O 8 + ionic core weakly bound to an oxygen molecule.

A novel experimental technique is described in which radiation from a free electron laser is used to measure infrared spectra of gas-phase cluster ions via vibrational predissociation of the corresponding ion–messenger atom complexes. The weakly bound complexes are formed in a temperature-controllable, radio frequency ion trap. This technique is applied to the study of the vibrational spectroscopy of the monovanadium oxide cluster cations VO+, VO2+, and VO3+.

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The vibrational spectroscopy of the mono- and divanadium oxide cluster cations VO(1-3)+ and V2O(2-6)+ is studied in the region from 600 to 1600 wave numbers by infrared photodissociation of the corresponding cluster cation-helium atom complexes. The comparison of the experimental depletion spectra with the results of density functional calculations on bare vanadium oxide cluster cations allows for an unambiguous identification of the cluster geometry in most cases and, for VO(1-3)+ and V2O(5,6)+, also of the electronic ground state. A common structural motif of all the studied divanadium cluster cations is a four-membered V-O-V-O ring, with three characteristic absorption bands in the 550-900 wave number region. For the V-O-V and V=O stretch modes the relationship between vibrational frequencies and V-O bond distances follows the Badger rule.