Predissociation spectroscopy of the argon-solvated H5O2+ “zundel” cation in the 1000–1900 cm−1 region

Predissociation spectra of the H5O2+⋅Ar1,2 cluster ions are reported in the 1000–1900 cm−1 region. The weakly bound argon atoms enable investigation of the complex in a linear action mode, and the resulting spectra are much simpler than those reported previously in this region [Asmis et al., Science 299, 1375 (2003) and Fridgen et al., J. Phys. Chem. A 108, 9008 (2004)], which were obtained using infrared multiphoton dissociation of the bare complex. The observed spectrum consists of two relatively narrow bands at 1080 and 1770 cm−1 that are likely due to excitation of the shared proton and intramolecular bending vibrations of the two water molecules, respectively. The narrow linewidths and relatively small (60 cm−1) perturbation introduced by the addition of a second argon atom indicate that the basic “zundel” character of the H5O2+ ion survives upon complexation.