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"Assigning Predissociation Infrared Spectra of
Microsolvated Hydronium Cations H3O+ . (H2)n,
n = 0, 1, 2, 3 by Ab Initio Molecular Dynamics." Marcel Baer, Dominik Marx, and Gerald MathiasChemPhysChem Abstract: Messenger predissociation spectroscopy is an important experimental method to obtain vibrational spectra of molecular ions or complexes such as protonated water clusters H+ . (H2O)n in the gas phase. However, the molecular properties and thus the linear infrared spectra may be modifi ed upon microsolvation with typical messengers such as H2 molecules or noble gas atoms. Employing ab initio molecular dynamics for the H2-microsolvated hydronium ion, we investigate these e ffects explicitly as a function of an increasing number of messengers up to filling the first microsolvation shell, i.e. for H3O+ . (H2)n, n = 0, 1, 2, 3 It is found that microsolvation with H2 lowers the inversion barrier of the hydronium core, which governs the inversion tunnel splitting due to umbrella motion, thus accelerating the inversion dynamics. By comparison to experiment a com- prehensive band assignment for the O--H stretch region is given thereby explaining the observed blue--shift of stretching bands upon increasing n. Furthermore, detailed analyses reveal intricate intra-- and intermolecular anharmonic mode couplings induced by the messengers, which yield a rich vibrational dynamics in these, at first glance, simple systems. Finally, the virtues but also the shortcomings of the ab initio molecular dynamics approach to vibrational spectroscopy are discussed. BMO authors (in alphabetic order): Gerald Mathias  WWW-Version |