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  • 1
    Electronic Resource
    Electronic Resource
    Theoretical and experimental investigation of the reaction BH+D2→BHD2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 479-488 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rate of the association reaction, BH+D2→BHD2 is determined both theoretically and experimentally. In the theoretical calculations, potential-energy surface information is obtained using multiconfiguration self-consistent-field and large-scale multireference configuration-interaction calculations with large correlation consistent basis sets. The preferred direction of approach is found to be along a non-least-motion pathway for which the BH and DD bonds come in nearly parallel to one another. The small computed activation energy of 2.6 kcal/mol for this highly exothermic reaction is found to arise almost exclusively from changes in zero-point vibrational energy. The experimental measurements of the BH disappearance rate are made at temperatures from 298 to 597 K and are shown to be only weakly dependent on total pressure over the range of 1–100 Torr. As a test of the proposed mechanism, we observe the growth of BD and find the BD appearance rate constant to be in excellent agreement with that for BH disappearance. The measured reaction rates are compared to the results of canonical variational transition-state theory calculations of the association rate and are found to be in excellent agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459547
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  • 2
    Electronic Resource
    Electronic Resource
    Homogeneous nucleation in supersaturated vapors of polar molecules: Acetonitrile, benzonitrile, nitromethane, and nitrobenzene (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3356-3368 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The critical supersaturations (Sc) required for the homogeneous nucleation of acetonitrile, benzonitrile, nitromethane, and nitrobenzene vapors have been measured over wide temperature ranges using a thermal diffusion cloud chamber. At Tr=0.44, the experimental results are higher than the predictions of the classical nucleation theory by 20% (CH3NO2), 50% (CH3CN), 57% (C6H5NO2), and 112% (C6H5CN). This trend correlates well with the dipole moments and to a lesser extent with the polarizabilities of these substances. Corresponding states of simple fluids and scaled nucleation law show that CH3CN and CH3NO2 have similar nucleation behavior which is different from that of C6H5CN and C6H5NO2. Correlations with other less polar substances are examined. The scaled law, with Ω (the excess surface entropy per molecule) determined from the temperature dependence of the bulk surface tension, gives a better description of the experimental results than the classical theory with the exception of nitromethane. The results suggest that the classical theory does not take proper account of the dipole–dipole interaction in calculating the free energy of the embryonic droplets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464108
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  • 3
    Electronic Resource
    Electronic Resource
    Recent advances in photoacoustic calorimetry: Theoretical basis and improvements in experimental design (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5381-5389 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Recent developments in time-resolved photoacoustic calorimetry (PAC) are discussed. An equation is derived relating the amplitude of the maximum photoacoustic signal to parameters of a photoacoustic cell, to physical properties of the solvents, and to the energy deposited as heat. The equation is validated by a series of scaling experiments: it correctly correlates the dependence of the PAC signal on cell thickness, on energy deposition, and on solvent properties. The dominant sources of background signal have been determined and the background signal reduced substantially relative to previous work. It is now possible to measure energies and lifetimes of transients in solutions with optical densities as low as ∼5×10−4. Data are presented for the energy of 2-cyclopentenone triplet, a transient for which interpretable PAC measurements were previously not possible. Its triplet energy is 73.1±1.1 kcal/mole. With reduced background and a faster digital storage oscilloscope, a quite short transient lifetime, 7.53±0.2 ns, and a triplet energy of 51.0±2.1 kcal/mol have been measured for 1,1-bis-(p-bromophenyl)ethene. The lifetime agrees very well with that determined by kinetic absorption spectroscopy and the triplet energy agrees with expectation based on the unsubstituted 1,1-diphenylethene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143407
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