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419 results on '"Thompson, Ward H."'

102. Time-Dependent Fluorescence in Nanoconfined Solvents. A Smoluchowski Equation Model Study

Author

Feng, Xiaobing and Thompson, Ward H.

Abstract

Time-dependent fluorescence (TDF) measurements are frequently used to probe solvation dynamics in nanoconfined solvents. It was previously found [J. Chem. Phys.2002, 117, 6618] in simple model systems that long time scales can arise in the TDF signal due to diffusion of the solute chromophore. Here, the effects of solute diffusion after electronic excitation on the TDF signal are studied using a generalized Smoluchowski equation. In this approach, the probability density in terms of the solute radial position and a collective solvent coordinate is determined as a function of time after excitation. Model one-dimensional free energy curves with a single barrier in the solute coordinateappropriate for relatively small, e.g., ∼2 nm diameter, cavities or poresare used to construct the full two-dimensional free energy surface and probe different physical models. The effects of position-dependence of diffusion coefficients and solvent coordinate force constants are also considered. The results indicate that the inclusion of radial diffusion leads to rich phenomena in the TDF. The position dependence of the diffusion coefficients is also found to have significant effects on the solute diffusion and solvation dynamics relevant to TDF. The results allow the comparison of the characteristics of the TDF signal predicted by different physical models that have been proposed to account for the long-time decays found for measurements in nanoconfined solvents.

Published
2024
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112. Determinants of Activity at Human Toll-like Receptors 7 and 8: Quantitative Structure–Activity Relationship (QSAR) of Diverse Heterocyclic Scaffolds

Author

Yoo, Euna, primary, Salunke, Deepak B., additional, Sil, Diptesh, additional, Guo, Xiaoqiang, additional, Salyer, Alex C. D., additional, Hermanson, Alec R., additional, Kumar, Manoj, additional, Malladi, Subbalakshmi S., additional, Balakrishna, Rajalakshmi, additional, Thompson, Ward H., additional, Tanji, Hiromi, additional, Ohto, Umeharu, additional, Shimizu, Toshiyuki, additional, and David, Sunil A., additional

Published
2014
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136. Structure, dynamics and hydrogen bonding of acetonitrile in nanoscale silica pores.

Author

Thompson, Ward H.

Subjects
*ACETONITRILE, *SILICA nanoparticles, *HYDROGEN bonding, *MOLECULAR structure, *PORE size (Materials), *MOLECULAR dynamics
Abstract

Molecular dynamics simulations are used to investigate the behaviour of liquid acetonitrile confined within nm diameter silica pores. Different approaches for characterising the liquid structure in the pores are examined and compared. The effect of surface chemistry on the liquid layering at the pore interface is discussed based on simulations in pores with modified interactions. Finally, the dynamical properties, specifically acetonitrile reorientation, are also considered and their dependence on molecule position is probed. [ABSTRACT FROM AUTHOR]

Published
2015
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145. On the role of hydrogen-bond exchanges in the spectral diffusion of water.

Author

Piskulich, Zeke A., Laage, Damien, and Thompson, Ward H.

Subjects
*DIFFUSION, *CONDENSED matter, *ACTIVATION energy, *HYDROGEN bonding, *EXCHANGE
Abstract

The dynamics of a vibrational frequency in a condensed phase environment, i.e., the spectral diffusion, has attracted considerable interest over the last two decades. A significant impetus has been the development of two-dimensional infrared (2D-IR) photon-echo spectroscopy that represents a direct experimental probe of spectral diffusion, as measured by the frequency–frequency time correlation function (FFCF). In isotopically dilute water, which is perhaps the most thoroughly studied system, the standard interpretation of the longest timescale observed in the FFCF is that it is associated with hydrogen-bond exchange dynamics. Here, we investigate this connection by detailed analysis of both the spectral diffusion timescales and their associated activation energies. The latter are obtained from the recently developed fluctuation theory for the dynamics approach. The results show that the longest timescale of spectral diffusion obtained by the typical analysis used cannot be directly associated with hydrogen-bond exchanges. The hydrogen-bond exchange time does appear in the decay of the water FFCF, but only as an additional, small-amplitude (<3%) timescale. The dominant contribution to the long-time spectral diffusion dynamics is considerably shorter than the hydrogen-bond exchange time and exhibits a significantly smaller activation energy. It thus arises from hydrogen-bond rearrangements, which occur in between successful hydrogen-bond partner exchanges, and particularly from hydrogen bonds that transiently break before returning to the same acceptor. [ABSTRACT FROM AUTHOR]

Published
2021
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146. Theoretical calculation of photodetachment intensities for H3O

Author

Karlsson, Hans O, Thompson, Ward H, Miller, William H, Karlsson, Hans O, Thompson, Ward H, and Miller, William H

Abstract

We have calculated total and arrangement-selected photodetachment intensities for the H3O- anion (and its deuterated form, D3O-) using a Green's function in a discrete variable representation with absorbing boundary conditions. A multiply-shifted quasiminimal residual method is used to obtain the Green's function for many energies at once. We present spectra obtained by explicitly treating two and four degrees of freedom. Comparison with experiment indicates that the bending angles in the anion and neutral are more similar than in the current potential energy surfaces. The calculated spectra are also consistent with the suggestion that the barrier should be ''earlier.'

Published
1996
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