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  • 1
    Electronic Resource
    Electronic Resource
    A potential-energy surface study of the 2A1 and low-lying dissociative states of the methoxy radical (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 311-322 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Low-lying bound and dissociative states of the methoxy radical have been studied at C3v conformations using accurate ab initio quantum chemical techniques. A double-zeta quality basis set augmented with polarization and diffuse functions has been used throughout. The A˜ 2A1 excited state is found to have an equilibrium conformation with RCO=1.614 A(ring), RCH=1.091 A(ring), and aitch-thetaHCO=102.6°, and the three a1 harmonic frequencies have been calculated (3239, 1308, and 733 cm−1). The following excitation energies have been estimated: A˜ 2A1 ← X˜ 2E vertical excitation, 4.21 eV; A˜ 2A1 → X˜ 2E vertical deexcitation, 3.52 eV; and the A˜–X˜ system origin, 3.96 eV. The surface intersections of the A˜ 2A1 state with three low-lying dissociative states (4A2, 2A2, and 4E) have been characterized. The threshold for predissociation has been estimated as 4.47 eV, corresponding to the 2A1–4A2 intersection. The rate of methoxy photolysis is estimated to be too small to warrant inclusion in atmospheric models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448801
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  • 2
    Electronic Resource
    Electronic Resource
    Reaction-path potential and vibrational frequencies in terms of curvilinear internal coordinates (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3188-3201 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a general formulation that allows physically intuitive curvilinear internal coordinates to be used for the calculation of potential energy expansions and generalized normal-mode vibrational frequencies in reaction-path calculations. The reaction path is defined, as usual, as the minimum-energy path in the mass-scaled Cartesian coordinate system, and curvilinear coordinates are used for vibrational frequency calculations at nonstationary points. The method is well adapted for use in variational transition state theory with semiclassical multidimensional tunneling (VTST/MT) approximations to calculate thermal rate constants. We present VTST/MT calculations for five reactions, H+H2→H2+H, O+H2→OH+H, CH3+H2→CH4+H, H+O2→HO2, and Cl+HBr→HCl+Br, to illustrate the use of the new curvilinear coordinates, and we compare the results to calculations employing rectilinear coordinates. We make detailed comparisons not only of the calculated rate constants but also of the vibrationally adiabatic ground-state potential energy curves and bound-state vibrational frequencies as functions of the reaction coordinate. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468630
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  • 3
    Electronic Resource
    Electronic Resource
    An ab initio investigation of possible intermediates in the reaction of the hydroxyl and hydroperoxyl radicals (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 5013-5024 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio quantum chemical techniques have been used to investigate covalently-bonded and hydrogen-bonded species that may be important intermediates in the reaction of hydroxyl and hydroperoxyl radicals. Stable structures of both types were identified. Basis sets of polarized double-zeta quality and large scale configuration interaction wave functions have been utilized. Based upon electronic energies, the covalently-bonded HOOOH species is found to be 26.4 kcal/mol more stable than the OH and HO2 radicals. Similarly, the hydrogen-bonded HO---HO2 species is found to have an electronic energy 4.7 kcal/mol below that of the component radicals, after correction is made for the basis set superposition error. The hydrogen-bonded form is found to be planar, to possess one relatively "normal'' hydrogen bond, and to have lowest energy 3A' and 1A' states that are essentially degenerate. The 1A‘ and 3A‘ excited states produced by rotation of the unpaired OH electron into the molecular plane are found to be very slightly bound.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450650
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  • 4
    Electronic Resource
    Electronic Resource
    Reaction-path dynamics in curvilinear internal coordinates including torsions (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 6491-6496 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We describe a procedure for calculating generalized normal mode vibrational frequencies along a reaction path in curvilinear coordinates for a polyatomic system involving torsions. We apply the method to calculate generalized normal mode frequencies and rate constants for the OH+H2→H2O+H reaction using variational transition state theory with a multidimensional semiclassical tunneling approximation for the transmission coefficient. The results are compared to rate calculations carried out in rectilinear Cartesian coordinates to test the sensitivity of the calculated thermal rate constants to the choice of coordinate. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471369
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  • 5
    Electronic Resource
    Electronic Resource
    The vibrational spectrum of H2O3: An ab initio investigation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5768-5779 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Theoretically determined frequencies and absorption intensities are reported for the vibrational spectra of the covalent HOOOH and hydrogen bonded HO...HOO intermediates that may form in the reaction of the hydroxyl and hydroperoxyl radicals. Basis sets of double-zeta-polarized quality, augmented by diffuse and second sets of polarization functions have been used with complete-active-space, self-consistent-field wave functions. The calculated harmonic vibrational frequencies of HOOOH have been corrected with empirical factors and presented in the form of a "stick'' spectrum. The oxygen backbone vibrations, predicted to occur at 519, 760, and 870 cm−1, are well separated from most interferences, and may be the most useful for the species' identification. In the case of the hydrogen bonded isomer, emphasis has been placed upon prediction of shifts in the intramolecular vibrational frequencies that take place upon formation of the complex. In particular, the HO stretch and HOO bend of HO2 are predicted to have shifts of −59 and 53 cm−1, respectively, which should facilitate their identification. It is also noted that the antisymmetric stretching frequency of the oxygen backbone in HOOOH exhibits a strong sensitivity to the degree of electron correlation, similar to that which has been previously observed for ozone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465928
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of the Coffee Mucilage Fermentation Process Using Chemical Indicators: A Field Study in Nicaragua (2005)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of food science 70 (2005), S. 0 
    Details
    ISSN: 1750-3841
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: : The recent “crisis” brought about by the collapse of the worldwide commodity coffee market has caused severe economic conditions for coffee producers in developing countries, including those of Central America. As a result, many coffee producers desire to improve the quality and consistency of their product to enter the specialty market. With the ultimate aim of assisting coffee producers in their quality control efforts, this study was designed to determine the feasibility of simple chemical measurements of the fermentation process on remote farms and to assess the potential of these measurements for assisting the producers in control and optimization efforts. Temperature, pH, and the concentrations of glucose, ethanol, and lactic acid were measured throughout the course of 7 coffee mucilage fermentation batches on 4 farms. In each batch, a pattern was observed in which the pH was initially in the range 5.5 to 5.7 and decreased sharply to about 4.6 as fermentation neared completion. Glucose concentration was seen to drop throughout the course of most batches, whereas either ethanol or lactic acid increased sharply near completion. The pH profile may prove useful in predicting the time of fermentation completion and in preventing over-fermentation of coffee mucilage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2621.2005.tb09960.x
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  • 7
    Electronic Resource
    Electronic Resource
    Accuracy of energy extrapolation in multireference configuration interaction calculations (1981)
    Springer
    Theoretical chemistry accounts 58 (1981), S. 81-96 
    Details
    ISSN: 1432-2234
    Keywords: Configuration interaction ; Selection of configurations ; Energy extrapolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The accuracy of extrapolation procedures in conjunction with energy-based configuration selection in CI calculations is examined. The normally high accuracy of such extrapolation can deteriorate in multireference CI calculations when configuration functions of low weight are included in the root (reference) set. This is due to the inadequacy of second-order energy contribution estimates for the very large number of discarded low-contribution functions generated as single and double excitations from the minor members of the root set. The problem may be overcome by increasing the number of configurations included in the zero-order function used for the energy contribution estimation process. Illustrative results are presented for excited states of the H2O molecule and the H2O+ ion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00550421
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  • 8
    Electronic Resource
    Electronic Resource
    Equivalence-restricted open-shell SCF theory (1974)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 8 (1974), S. 707-714 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is presented for generating open-shell equivalence-restricted SCF orbitals in high-symmetry situations using Roothaan-Hartree-Fock programs which are adapted for lower symmetry.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560080506
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