Small protonated water clusters, H+(H2O)n, in the gas-phase are believed by some to be the basic building blocks for conformations encountered in acidic aqueous solutions. Their study is propelled by improved molecular beam techniques that allow measuring colder clusters over wider frequency ranges. Up to n=5 it is believed that only the lowest-energy conformer contributes, which is a branched isomer based on an Eigen, H3O+, core for n=1,3,4,5 and a Zundel core, H2O�O�OH2, for n=2 and 6. Yet, presently some conspicuous discrepancies exist between experimental and theoretical spectra, the latter computed predominantly in the harmonic approximation that is inadequate for such highly anharmonic systems.We have computed the IR spectra from the dipole-dipole autocorrelation function of ab-initio molecular dynamic trajectories using the CP2K package, for both n=4 [1] and n=5 [2]. We have found that the conventional assignment based on a branched Eigen isomer is inadequate, and a higher energy linear isomer must also be contributing. Its core is either a Zundel core (for n=4) or an Eigen-Zundel hybrid (for n=5). These isomers are potentially interesting because they constitute of small 'proton wires' in the gas-phase.[1] Kulig and Agmon, J. Phys. Chem. B 2014, 11  8 , 278.[2] Kulig and Agmon, PCCP 2014, 1  6  , 4933.

Simulating the infrared spectra of small protonated water clusters

248th National Meeting (2014)

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