Insights into the dynamics of evaporation and proton migration in protonated water clusters from Large‐scale Born–Oppenheimer direct dynamics

Large‐scale on‐the‐fly Born–Oppenheimer molecular dynamics simulations using recent advances in linear scaling electronic structure theory and trajectory integration techniques have been performed for protonated water clusters around the magic number (H₂O)_nH⁺, for n = 20 and 21. Besides demonstrating the feasibility and efficiency of the computational approach, the calculations reveal interesting dynamical details. Elimination of water molecules is found to be fast for both cluster sizes but rather insensitive to the initial geometry. The water molecules released acquire velocities compatible with thermal energies. The proton solvation shell changes between the well‐known Eigen and Zundel motifs and is characterized by specific low‐frequency vibrational modes, which have been quantified. The proton transfer mechanism largely resembles that of bulk water but one interesting variation was observed. © 2012 Wiley Periodicals, Inc.     

The molecular structures of gaseous cyclopentene oxide,cyclohexene oxide and cycloheptene oxide as determined by electron diffraction

The molecular structures of gaseous cyclopentene oxide, cyclohexene oxide and cycloheptene oxide are investigated by electron diffraction. The boat conformation of cyclopentene oxide is confirmed, while a half-chair conformer is determined for cyclohexene oxide. Cycloheptene oxide is found to exist in a 66(2):34(2) conformational mixture of two chair forms.     

A Novel Calorimetric Approach to the Redox Thermochemistry of Non-stoichiometric Oxides enthalpy of Oxidation of La1−yCayCrO3−δ

A novel calorimetric approach to the energetics of redox reactions in non-stoichiometric oxides is presented. The method utilizes a step-wise heated adiabatic calorimeter for determination of average enthalpies of oxidation. The measurement uncertainty is dominated by the uncertainty in the determination of the mass increment due to the oxidation. An experimental investigation of the re-oxidation energetics of reduced La_1–yCa_yCrO_3– is presented. The variation of the average formal oxidation state with temperature and oxygen fugacity is calculated from the experimentally determined enthalpy of oxidation and an estimated (lattice and configurational) entropy of oxidation. The calculated curves are in good agreement with experimental determinations reported in literature.This revised version was published online in November 2005 with corrections to the Cover Date.     

Use of novel immobilized β-galactosidase reactor to hydrolyze the lactose constituent of skim milk

A novel chemical reactor, consisting of β-galactosidase fromAspergillus oryzae immobilized on a ribbed membrane made from polyvinyl-chloride and silica, was used to hydrolyze the lactose constituent of skim milk. Multiresponse nonlinear regression methods were employed to determine the kinetic parameters of rate expressions based on a proposed enzymatic mechanism that includes the formation of oligosaccharides. HPLC methods were employed to monitor the concentrations of all species present in the effluent stream. For the experimental conditions used in this research, a rate expression that includes the inhibition effect of α-galactose is sufficient to model the reaction network.     

Energetic mapping of Ni catalysts by detailed kinetic modeling

Temperature-programmed desorption (TPD) of CO has been performed on supported and unsupported nickel catalysts. The unsupported Ni catalyst consists of a Ni(14 13 13) single crystal which has been studied under ultrahigh vacuum conditions. The desorption energy for CO at low CO surface coverage was found to be 119 kJ/mol, and the binding energy of C to the Ni(111) surface of the crystal was 703 kJ/mol. The supported catalysts consist of nickel supported on hydrotalcite-like compounds with three different Mg2+/Al3+ ratios. The experimental results show that for the supported Ni catalysts TPD of CO leads to desorption of both CO and CO2, with the latter being dominant. Dissociation of CO takes place, and considerable amounts of residue C are left on the surface. The residue C is removed by temperature-programmed oxidation (TPO). The results show that a low Mg2+/Al3+ ratio in the hydrotalcite precursor seems to result in more steplike sites, kinks, and defects for carbon monoxide dissociation. A detailed kinetic modeling of the TPO results based on elementary reaction steps has been conducted to give an energetic map of supported Ni catalysts. Experimental results from the ideal Ni surface fit nicely with literature values, providing useful information for identifying active sites on supported Ni catalysts.     

Finite approximations of physical models over p-adic fields

We show that the p-adic Schrödinger operator, as defined in [7], can be approximated in a very strong sense by finite Schröinger operators.