Kinetics and Reaction Dynamics3975 Spontaneous appearance of chirally asymmetric steady states in a reaction model including imperfectly stereoselective, chirally autocatalytic reactions Kazutoshi Iwamoto 3980 Temperature dependence of ketyl radical in aqueous benzophenone solutions up to 400 C: A pulse radiolysis study
A comprehensive study of the proton vibrational dynamics in isolated (HX)m⋅(M)n (X=Cl, Br, and M=H2O, D2O, CH3OH) clusters is presented. Mid-IR (1900–3900 cm−1) spectra are measured in pulsed, seeded slit nozzle expansions. A close similarity among the HCl and HBr systems is revealed and exploited for cluster assignment. Distinct absorptions by small HX and mixed HX–M clusters are superimposed on broadbands, partly due to electrolytically dissociated HX in larger mixed clusters. Assignments of bands corresponding to mixed dimers and trimers based on their X–H and O–H stretching fundamentals are provided. The broad Cl–H stretching band profile of the 1:2 complex is indicative of sub-picosecond intracluster vibrational energy redistribution. The assignments are compared to matrix isolation experiments, when available. Systematic quantum chemistry calculations are performed for HCl–water complexes with up to three molecules and their isotopomers. Hydrogen bond induced frequency shifts of Cl–H stretching vibrations are best described at the coupled-cluster [CCSD(T)] level of theory. Lower level correlated quantum-chemical calculations clearly overestimate Cl–H frequency shifts. The low abundance of mixed clusters in the size range close to electrolytic dissociation (n=3–5) is discussed.
A comprehensive experimental study of the OH stretching vibrations of size-selected clusters of enantiopure and racemic methyl lactate is presented. For the size selection, we measured angular dependent mass spectra and time-of-flight distributions at the different fragment masses. In this way the fragmentation of these clusters upon electron impact ionization is obtained. The largest fragment masses of the neutral (MLac)n clusters are the protonated (MLac)n-1H+ ions. The results of a pressure dependent study in an FTIR jet experiment are compared with completely size-selected experiments based on atomic beam deflection and depletion spectroscopy. The size assignments and spectra agree for dimers and trimers. Structures and spectral information for the trimer and the tetramer at density functional and MP2 level are provided. Selective self-aggregation and chiral recognition was observed for homochiral trimers. They exhibit a ring structure bound by OH...OH hydrogen bonds. A spectacular switch in the hydrogen bonding topology was observed for the tetramer. The homochiral enantiomer exhibits cooperative OH...OH bonding, while the heterochiral version shows isolated OH...O=C bonding in a symmetric SRSR arrangement. The crucial ingredients for this identification are the size-selective IR spectra with their different shifts and line patterns which are reproduced by the calculations.
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