@article {1439, title = {Does atmospheric processing of saturated hydrocarbon surfaces by NO3 lead to volatilization?}, journal = {Geophysical Research Letters}, volume = {33}, number = {17}, year = {2006}, note = {ISI Document Delivery No.: 085ZJTimes Cited: 23Cited Reference Count: 28Knopf, D. A. Mak, J. Gross, S. Bertram, A. K.}, month = {Sep}, pages = {5}, type = {Article}, abstract = {The heterogeneous oxidation of a saturated hydrocarbon monolayer by NO3 was studied. A flow tube reactor coupled to chemical ionization mass spectrometry was used to determine the reactive uptake coefficient of NO3 on these surfaces, and X-ray photoelectron spectroscopy (XPS) was used to investigate surface oxidation and to determine if exposure to NO3 leads to volatilization of the organic substrate. The uptake coefficient of NO3 by an alkane monolayer is about (8.8 +/- 2.5) x 10(-4), which may lead to competitive oxidation compared with OH, due to the higher atmospheric abundance of NO3 under certain conditions. The XPS results are consistent with the formation of 1) C-O groups, 2) ketones or aldehydes, and 3) carboxylic groups. The XPS results also suggest that NO3 does not rapidly volatilize the organic surface: even under extremely polluted conditions, maximum 10\% of the organic layer is volatilized.}, keywords = {FILMS, GAS-PHASE PRODUCTS, HETEROGENEOUS REACTION, KINETICS, LIQUID, OLEIC-ACID, ORGANIC AEROSOLS, ozone, PARTICLES, REACTIVE UPTAKE}, isbn = {0094-8276}, url = {://000240642600004}, author = {Knopf, D. A. and Mak, J. and Gross, S. and Bertram, A. K.} } @article {1521, title = {Why tert-butyl alcohol associates in aqueous solution but trimethylamine-N-oxide does not}, journal = {Journal of Physical Chemistry B}, volume = {110}, number = {21}, year = {2006}, note = {ISI Document Delivery No.: 046XRTimes Cited: 14Cited Reference Count: 41}, month = {Jun}, pages = {10514-10518}, type = {Article}, abstract = {In dilute aqueous solution, tert-butyl alcohol (TBA) tends to aggregate but trimethylamine-N-oxide ( TMAO) does not. Given that both molecules have very similar geometry with hydrophobic and hydrophilic groups, it is interesting to ask why they behave so differently in aqueous solution. To explore this question, we use molecular dynamics simulations to study two models representing TBA and TMAO that differ essentially only in their electrostatic properties. It is shown that this difference is sufficient to give the different solution behavior. Furthermore, the principal difference identified is that the hydrophilic group of TMAO ( the oxygen) interacts on average much more strongly with water than the corresponding group ( the hydroxyl) of TBA. A hydrogen-bond analysis shows that water-TBA and water-TMAO hydrogen bonds are similar in number, but that the hydrogen-bond energy is much more negative for water-TMAO. In all likelihood, this accounts for the different behavior in dilute aqueous solution.}, keywords = {BINARY-MIXTURES, CLATHRATE HYDRATE FORMATION, ELECTROLYTE SOLUTIONS, HYDROGEN-BOND DYNAMICS, HYDROPHOBIC INTERACTIONS, LIGHT-SCATTERING, LIQUID, MOLECULAR-DYNAMICS, SIMULATION, WATER MIXTURES}, isbn = {1520-6106}, url = {://000237844900046}, author = {Paul, S. and Patey, G. N.} } @article {5109, title = {Mixing schemes for aqueous dimethyl sulfoxide: Support by X-ray diffraction data}, journal = {Journal of Solution Chemistry}, volume = {30}, number = {10}, year = {2001}, note = {ISI Document Delivery No.: 505UTTimes Cited: 19Cited Reference Count: 18}, month = {Oct}, pages = {885-893}, type = {Article}, abstract = {Aqueous dimethyl sulfoxide (DMSO) was studied by X-ray diffraction at room temperature. The results indicated that there are three distinct composition regions. In the DMSO-rich region, DMSO molecules retain the same molecular arrangement as in the pure, state, while H2O does not show any structural feature. These findings are in the complete agreement with the suggestion by our earlier thermodynamic study on aqueous DMSO.((1)) In the H2O-rich region, there is an indication that DMSO molecules exist as small clusters bound mainly by S=O dipole attraction. Hence, hydrophobic CH3 groups point outward from such a cluster and DMSO acts in effect as a hydrophobic solute. This is also consistent with the findings of our earlier thermodynamic study. In the intermediate region, a gradual change in the radial distribution function with composition was observed.}, keywords = {aqueous DMSO, DIMETHYLSULFOXIDE, intensity, LIQUID, MIXING SCHEMES, NEUTRON-DIFFRACTION, PARTIAL MOLAR ENTHALPIES, WATER MIXTURES, x-ray diffraction}, isbn = {0095-9782}, url = {://000172934500003}, author = {Koga,Yoshikata and Kasahara, Y. and Yoshino, K. and Nishikawa, K.} } @article {4749, title = {Isotropic fluid phases of dipolar hard spheres}, journal = {Physical Review Letters}, volume = {84}, number = {1}, year = {2000}, note = {ISI Document Delivery No.: 271HJTimes Cited: 86Cited Reference Count: 28}, month = {Jan}, pages = {115-118}, type = {Article}, abstract = {Monte Carlo simulations are used to calculate the equation of state and free energy-of dipolar hard sphere fluids at low temperatures and densities. Evidence for the existence of isotropic-fluid-isotropic-fluid phase transitions is presented and discussed. Condensation in the dipolar hard sphere fluid is unusual in that it is not accompanied by large energy or entropy changes. An explanation of this behavior is put forward.}, keywords = {CLUSTERS, COMPUTER-SIMULATION, CONDENSATION, LIQUID, orientational order, SYSTEMS}, isbn = {0031-9007}, url = {://000084587900029}, author = {Camp, P. J. and Shelley, J. C. and Patey, G. N.} } @article {4748, title = {Structure and scattering in colloidal ferrofluids}, journal = {Physical Review E}, volume = {62}, number = {4}, year = {2000}, note = {ISI Document Delivery No.: 365YATimes Cited: 67Cited Reference Count: 32Part B}, month = {Oct}, pages = {5403-5408}, type = {Article}, abstract = {The structure of a model colloidal ferrofluid, the dipolar hard-sphere fluid, at low temperature has been investigated using Monte Carlo simulations. Extensive particle association into chainlike and ringlike clusters is observed at low density. The structure factors have been calculated, and are analyzed with the aid of simple scaling arguments. We describe the progression of fluid structures from the low-density associated phase, to the high-density liquid phase. This paper may he of help in obtaining an experimental observation of a fluid-fluid transition in colloidal ferrofluids.}, keywords = {DIPOLAR HARD-SPHERES, FLUIDS, LIQUID, LIVING, LOW-DENSITIES, MODEL POLAR CLUSTERS, MONTE-CARLO, orientational order, PHASES, POLYMERS, SYSTEMS}, isbn = {1063-651X}, url = {://000089977000025}, author = {Camp, P. J. and Patey, G. N.} } @article {3177, title = {EQUATION-OF-MOTION FOR 2 COUPLED SPIN-1 NUCLEI UNDER A COHERENT AND RANDOM HAMILTONIAN}, journal = {Physical Review B}, volume = {50}, number = {13}, year = {1994}, note = {ISI Document Delivery No.: PL412Times Cited: 8Cited Reference Count: 27}, month = {Oct}, pages = {9245-9257}, type = {Article}, abstract = {The time dependence of the density operator for two coupled spin-1 nuclei, such as dideuterium D2 and dinitrogen N-14(2), under the second rank intramolecular dipolar and the first rank spin-rotation Hamiltonians has been derived. It is shown that the relaxation rates for the ortho and para species are not identical. We report the five independent rates for the para and the 21 independent rates for the ortho species. Due to cross relaxation between spin orders which precess at a common frequency, the relaxation for the ortho configuration is not always single exponential. There are 15 cross-relaxation terms between certain spin orders for the ortho species in the slow-motion regime. The complexity of our coupled spin system is discussed for the solid and the Jeener-Broekaert echo sequences. The Zeeman spin-lattice relaxation rates R10 for ortho- and para-dideuterium have been measured experimentally in partially oriented nematic solvents at 304 K using H-2 NMR. The solvents used are PCH-7, 1132, and a 55 wt\% 1132/EBBA mixture. These oriented solvents make it possible to separate the resonances of the ortho and para configurations thereby facilitating the R10 determination directly without multiexponential analysis. The R10 of para-dideuterium is about twice that of ortho-dideuterium in all experiments. Using our calculated expressions for R10 based on quadrupolar, dipolar, and spin-rotation interactions, and performing the proper averaging over the rotational states, we obtain excellent agreement with our experimental results. Good agreement has been obtained with published low-temperature studies as well.}, keywords = {D2, HD, LIQUID, MAGNETIC-RESONANCE, MOLECULES, relaxation, SOLVENTS, SPECTRA}, isbn = {0163-1829}, url = {://A1994PL41200032}, author = {ter Beek, L. C. and Burnell, E. E.} } @article {2994, title = {GROUND-STATE CONFIGURATIONS OF MODEL MOLECULAR CLUSTERS}, journal = {Journal of Chemical Physics}, volume = {100}, number = {3}, year = {1994}, note = {ISI Document Delivery No.: MU316Times Cited: 24Cited Reference Count: 32}, month = {Feb}, pages = {2213-2219}, type = {Article}, abstract = {We have determined the ground state configurations of model molecular dipolar clusters using Monte Carlo simulations. Cluster sizes ranged from N=3 to N=20. The molecular models consisted of spherically symmetric hard sphere or Lennard-Jones interactions, as well as dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. Molecular polarizability was also included in some calculations. We first found the ground state configurations of dipolar hard sphere clusters, and then systematically increased the quadrupole moment and molecular polarizability from zero up to typical values for small molecules. The relevance of our results to real molecular clusters is discussed.}, keywords = {COMPUTATIONS, DYNAMICS, HYDROGEN-FLUORIDE CLUSTERS, LENNARD-JONES CLUSTERS, LIQUID, MONTE-CARLO, OPTIMIZATION, SIMULATION, STABILITY}, isbn = {0021-9606}, url = {://A1994MU31600043}, author = {Clarke, A. S. and Patey, G. N.} }