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Articles 331 - 340 of 340
Full-Text Articles in Chemistry
Condensation Of Supersaturated Vapors Of Hydrogen Bonding Molecules: Ethylene Glycol, Propylene Glycol, Trimethylene Glycol, And Glycerol, David B. Kane, M. Samy El-Shall
Condensation Of Supersaturated Vapors Of Hydrogen Bonding Molecules: Ethylene Glycol, Propylene Glycol, Trimethylene Glycol, And Glycerol, David B. Kane, M. Samy El-Shall
Chemistry Publications
The critical supersaturations required for the homogeneous nucleation (rate of 1 drop cm−3 s−1) of ethylene glycol, propylene glycol, trimethylene glycol and glycerol vapors have been measured over wide temperature ranges (e.g., 280–400 K) using an upward thermal diffusion cloud chamber. At lower temperatures the experimental nucleation rates are much higher than the predictions of the classical nucleation theory. Glycerol shows the best agreement between experiment and theory in the temperature range of 340–370 K. An apparent increase in the critical supersaturation of glycerol is observed with increasing carrier gas (helium) pressure and this effect is more …
Oxidation States And Magnetism Of Fe Nanoparticles Prepared By A Laser Evaporation Technique, B. J. Jönsson, T. Turkki, V. Ström, M. S. El-Shall, K. V. Rao
Oxidation States And Magnetism Of Fe Nanoparticles Prepared By A Laser Evaporation Technique, B. J. Jönsson, T. Turkki, V. Ström, M. S. El-Shall, K. V. Rao
Chemistry Publications
Nanoparticles of iron and iron oxide have been prepared in a thermal diffusion cloud chamber using pulsed laser evaporation. SEM/TEM studies of these particles reveal a size distribution with a mean diameter of about 60 Å. This is consistent with the mean particle size estimated from the magnetic data. The oxidation levels of these nanoparticles prepared at different partial oxygen pressures were investigated using FTIR. All the samples are found to exhibit superparamagnetism with blocking temperatures ranging from 50 K to above room temperature. Magnetic anisotropy constants are calculated from the frequency dependence of the blocking temperatures are found to …
Gas Phase Clustering Of N2 Molecules On To Tio+: Comparison With Ti+ And Evidence For The Octahedral Structure Of Tio+(N2)5, George M. Daly, M. Samy El-Shall
Gas Phase Clustering Of N2 Molecules On To Tio+: Comparison With Ti+ And Evidence For The Octahedral Structure Of Tio+(N2)5, George M. Daly, M. Samy El-Shall
Chemistry Publications
A striking difference in the clustering efficiency of Ti+ and TiO+ toward N2 or O2 has been observed in a laser vaporizationhigh pressure mass spectrometric source. Evidence for the magic number n=5 within the sequence TiO+(N2) n is presented. The results are consistent with an octahedral structure for TiO+(N2)5.
Ab Initio Equilibrium Constants For H2o–H2o And H2o–Co2, Nancy Renyou Zhang, Donald D. Shillady
Ab Initio Equilibrium Constants For H2o–H2o And H2o–Co2, Nancy Renyou Zhang, Donald D. Shillady
Chemistry Publications
Ab initio 6‐31G** electronic structure calculations have been used to determine the minimum energy geometries and vibrational frequencies of molecular clusters of water and carbon dioxide. Application of statistical thermodynamics leads to theoretical equilibrium constants for gas phase dimerization of water and the formation of an adduct of carbon dioxide with water.The low energy vibrations of the clusters lead to much larger contributions to the vibrational partitioning of the energy than do the fundamental vibrations of the monomeric species. A new ‘‘Harmonic‐Morse’’ formula is derived to estimate anharmonicity from optimized harmonic frequencies and two additional values on the potential surface …
Monte Carlo Simulation Of Acetonitrile Clusters [Ch3cn] N , N=2–256: Melting Transitions And Even/Odd Character Of Small Clusters (N=2–9), Heat Capacities, Density Profiles, Fractal Dimension, Intracluster Dimerization, And Dipole Orientation, D. Wright, M. Samy El-Shall
Monte Carlo Simulation Of Acetonitrile Clusters [Ch3cn] N , N=2–256: Melting Transitions And Even/Odd Character Of Small Clusters (N=2–9), Heat Capacities, Density Profiles, Fractal Dimension, Intracluster Dimerization, And Dipole Orientation, D. Wright, M. Samy El-Shall
Chemistry Publications
The thermodynamic and structural properties of acetonitrile clusters [CH3CN] N , N=2–15, 20, 30, 60, 128, and 256 have been investigated using Monte Carlo simulation. Interactions in the small clusters (N≤9) are dominated by antiparallel pairing of the molecular dipoles. The simulations reveal rigid ↔ fluid (melting) transitions with a remarkable even–odd alternation in the transition temperatures for the N=2–9 clusters. The higher melting temperatures of the even‐N clusters arise as consequences of the antiparallel paired dipoles which provide favorable electrostatic interactions. Even–odd alternation has also been observed in the configurational energies and …
Homogeneous Nucleation In Supersaturated Vapors Of Polar Molecules: Acetonitrile, Benzonitrile, Nitromethane, And Nitrobenzene, D. Wright, R. Caldwell, C. Moxely, M. S. El-Shall
Homogeneous Nucleation In Supersaturated Vapors Of Polar Molecules: Acetonitrile, Benzonitrile, Nitromethane, And Nitrobenzene, D. Wright, R. Caldwell, C. Moxely, M. S. El-Shall
Chemistry Publications
The critical supersaturations (S c ) 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 T r =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 …
Analysis Of Homogeneous Nucleation Data Of Polar Molecules: Vapor Association, Dipole Orientation, And Elongated Clusters, D. Wright, M. S. El-Shall
Analysis Of Homogeneous Nucleation Data Of Polar Molecules: Vapor Association, Dipole Orientation, And Elongated Clusters, D. Wright, M. S. El-Shall
Chemistry Publications
In this paper we present the results of several theoretical models examined in order to explain the observed systematic deviations of the homogeneous nucleation of highly polar substances from the predictions of the classical nucleation theory (CNT). It is found that molecular association in acetronitrile or nitromethane vapor cannot explain the observed higher supersaturations. Similarly, the use of virial coefficient data to obtain a size dependent surface energy correction factor does not reproduce the experimental results. It is shown that orientation of the surface dipoles within the spherical droplets results in higher supersaturations in agreement with the experimental findings. We …
Observation Of Eliminative Cationic Polymerization Within Van Der Waals Clusters, M. Samy El-Shall, K. E. Schriver
Observation Of Eliminative Cationic Polymerization Within Van Der Waals Clusters, M. Samy El-Shall, K. E. Schriver
Chemistry Publications
We report the first observation of eliminative cationic polymerization within van der Waals (vdW) clusters following electron impact ionization at pressures of 10−8 Torr. The elimination reactions of C2H3Cl+ within the clusters terminate after three successive steps, each involving elimination of HCl or Cl. The results provide a mechanism for the early stages of gas phase cationic polymerization of vinyl chloride and demonstrate the feasibility of using vdW clusters as a means of studying gas phase cationic polymerization.
Magnetic And Mössbauer Study Of Metal‐Zeolite Interaction In Catalysts, Thomas Pannaparayil, M. Oskooie-Tabrizi, C. Lo, L. N. Mulay, G. A. Melson, V. U. S. Rao
Magnetic And Mössbauer Study Of Metal‐Zeolite Interaction In Catalysts, Thomas Pannaparayil, M. Oskooie-Tabrizi, C. Lo, L. N. Mulay, G. A. Melson, V. U. S. Rao
Chemistry Publications
Molecular sieve aluminosilicates, such as ZSM‐5 and mordenite, when impregnated with highly dispersed Fe, yield catalysts for the selective conversion of coal‐derived syngas (CO+H2) to liquid hydrocarbon fuels. Fe performs the primary Fischer‐Tropsch (FT) syngas to yield light olefins which are converted by the acidic (H+) and shape‐selective function of the zeolite to high octane gasoline components. The physical aspects of the Fe‐mordenite interaction studied by magnetic measurements, Mössbauer, and IR spectroscopy are reported and correlations with the catalytic properties are drawn. Mordenite samples with [SiO2/Al2O3] ratio in the range …
Collisional Depolarization Of State Selected (J,M J ) Bao A 1Σ+ Measured By Optical–Optical Double Resonance, Stuart J. Silvers, Richard A. Gottscho, Robert W. Field
Collisional Depolarization Of State Selected (J,M J ) Bao A 1Σ+ Measured By Optical–Optical Double Resonance, Stuart J. Silvers, Richard A. Gottscho, Robert W. Field
Chemistry Publications
The optical–optical double resonance (OODR) technique is used to investigate the change in magnetic quantum number (M) a state selected molecule undergoes on collision with other molecules. A first linearly polarized dye laser prepares A 1Σ+BaO(v = 1) in the J = 1, M = 0 sublevel. The extent of collisional transfer to other M sublevels of both J = 1 and J = 2 is then probed by a second polarized dye laser which induces fluorescence from the C 1Σ+ state. Elastic collisions (ΔJ = 0) between BaO (A …