The Journal of Chemical Physics · 2003 · 87 citations · 71 references
EngineeringAcidic ProtonsComputational ChemistryChemistrySlit Nozzle ExpansionsSpectra-structure CorrelationCluster AssignmentProton Vibrational DynamicsPhysicsBiochemistryPhysical ChemistryHydrogenQuantum ChemistryMolecular ChemistryHbr–solvent ComplexesNatural SciencesProton TransferHydrogen BondCluster ChemistryMolecular ComplexSmall Hcl–
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.
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