期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 133, 期 11, 页码 4062-4072出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja1099209
关键词
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资金
- Deutsche Forschungsgemeinschaft [DFG MA 1547/8]
- Research Department Interfacial Systems Chemistry (RD IFSC) at RUB
- Fonds der Chemischen Industrie (FCI)
Understanding chemical reactivity at ultracold conditions, thus enabling molecular syntheses via interstellar and atmospheric processes, is a key issue in cryochemistry. In particular, acid dissociation and proton transfer reactions are ubiquitous in aqueous microsolvation environments. Here, the full dissociation of a HCl molecule upon stepwise solvation by a small number of water molecules at low temperatures, as relevant to helium nanodroplet isolation (HENDI) spectroscopy, is analyzed in mechanistic detail. It is found that upon successive aggregation of HCl with H2O molecules, a series of cyclic heteromolecular structures, up to and including HCl(H2O)(3), are initially obtained before a precursor state for dissociation, HCl(H2O)(3)center dot center dot center dot H2O, is observed upon addition of a fourth water molecule. The latter partially aggregated structure can be viewed as an activated species, which readily leads to dissociation of HCl and to the formation of a solvent-shared ion pair, H3O+(H2O)(3)Cl. Overall, the process is mostly downhill in potential energy, and, in addition, small remaining barriers are overcome by using kinetic energy released as a result of forming hydrogen bonds due to aggregation. The associated barrier is not ruled by thermal equilibrium but is generated by athermal non-equilibrium dynamics. These aggregation-induced chemical reactions are expected to be of broad relevance to chemistry at ultralow temperature much beyond HENDI spectroscopy.
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