Showing papers by "Peter J. Rossky published in 2005"

Role of water in electron-initiated processes and radical chemistry: issues and scientific advances.

Abstract: Chemical Science Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352; Department of Chemistry, ShelbyHall, University of Alabama, Box 870336, Tuscaloosa, Alabama 35487-0336; Notre Dame Radiation Laboratory, University of Notre Dame,Notre Dame, Indiana 46556; Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 0520-8107; Argonne NationalLaboratory, 9700 South Cass Avenue, Argonne, Illinois 60439; Department of Computer Science and Department of Physics, 2710 University Drive,Washington State University, Richland, Washington 99352-1671; Lawrence Berkeley National Laboratory, 1 Cyclotron Road Mailstop 1-0472,Berkeley, California 94720; Department of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station A5300,Austin, Texas 78712; Office of Basic Energy Sciences, U.S. Department of Energy, SC-141/Germantown Building, 1000 Independence Avenue,S.W., Washington, D.C. 20585-1290; Department of Physics and Engineering Physics, Stevens Institute of Technology, Castle Point on Hudson,Hoboken, New Jersey 07030; Department of Chemistry, Johns Hopkins University, 34th and Charles Streets, Baltimore, Maryland 21218;Department of Chemistry, University of Southern California, Los Angeles, California 90089-1062; Department of Chemistry, The Ohio StateUniversity, 100 West 18th Avenue, Columbus, Ohio 43210-1185; Department of Chemistry, Columbia University, Box 3107, Havemeyer Hall,New York, New York 10027; Department of Chemistry, University of Pittsburgh, Parkman Avenue and University Drive,Pittsburgh, Pennsylvania 15260; Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000; Department of Physics andAstronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, New Jersey 08854-8019; Department of Chemistry,516 Rowland Hall, University of California, Irvine, Irvine, California 92697-2025; Stanford Synchrotron Radiation Laboratory, Stanford LinearAccelerator Center, 2575 Sand Hill Road, Mail Stop 69, Menlo Park, California 94025; School of Chemistry and Biochemistry, Georgia Institute ofTechnology, 770 State Street, Atlanta, Georgia 30332-0400; Geology Department, University of California, Davis, One Shields Avenue,Davis, California 95616-8605; Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue,Cambridge, Massachusetts 02139-4307; Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084Received July 23, 2004

Characterization of Excess Electrons in Water-Cluster Anions by Quantum Simulations

Abstract: Water-cluster anions can serve as a bridge to understand the transition from gaseous species to the bulk hydrated electron. However, debate continues regarding how the excess electron is bound in \((\mathrm{H}_{2}\mathrm{O})_{n}^{-}\) , as an interior, bulklike, or surface electronic state. To address the uncertainty, the properties of \((\mathrm{H}_{2}\mathrm{O})_{n}^{-}\) clusters with 20 to 200 water molecules have been evaluated by mixed quantum-classical simulations. The theory reproduces every observed energetic, spectral, and structural trend with cluster size that is seen in experimental photoelectron and optical absorption spectra. More important, surface states and interior states each manifest a characteristic signature in the simulation data. The results strongly support assignment of surface-bound electronic states to the water-cluster anions in published experimental studies thus far.

Static and dynamic quantum effects in molecular liquids: a linearized path integral description of water.

Abstract: Structure, transport properties, and IR spectra including quantum effects are calculated for a flexible simple point charge model of liquid water. A recently introduced combination of a variational local harmonic description of the liquid potential surface and the classical Wigner approximation for the dynamics is used. The potential energy and interatomic radial distribution functions are in good agreement with accurate results from the literature and are significantly closer to experiment than predictions found from classical theory. The oxygen and hydrogen velocity correlation functions are also calculated, and the corresponding molecular diffusion coefficient is in good accord with existing theoretical estimates including quantum effects. Of most interest, an ab initio quantum correction factor is obtained to correct the far IR spectrum of water. When corrected, a spectrum based on a classical simulation yields results that agree well with experiment. Combined with internal tests of consistency, these observations indicate that this quite flexible approach will be effective for a variety of molecular problems involving the dynamics of light nuclei.

Origins of nonexponential decay in single molecule measurements of rotational dynamics.

Abstract: Recent reports have demonstrated that the correlation function of the fluorescence dichroism signal, measured as a probe of single molecule rotational dynamics, should not manifest a single exponential decay even for isotropic diffusion. This has called into question the attribution of observed nonexponential behavior in supercooled fluids and polymer systems to dynamical heterogeneity. We show here that, for the case of a high numerical aperture objective, the dichroism decay becomes indistinguishable from a single exponential. As a consequence, observed nonexponential decays can be associated with complex rotational dynamics. These effects are illustrated via simulated rotational trajectories for isotropic diffusion of a dipole.

Response to Comment on "Characterization of Excess Electrons in Water-Cluster Anions by Quantum Simulations"

Abstract: We reiterate that the conclusions of our original report are based on identifiable characteristic trends in several observables with cluster size. The numerical comparison between simulated and experimental vertical detachment energies emphasized by Verlet et al . reflect quantitative limitations of our atomistic model, but, in our opinion, do not undermine these conclusions.

Nano Mechanical Analysis of IFM Force Profiles on Self-Assembled Monolayers

Abstract: In this study, a defect-free, self-assembled monolayer of octadecyltrichlorosilane (OTS) was deposited on a silicon substrate. Nanoindentation experiments were performed with an interfacial force microscope (IFM) on these 2.5 nm monolayers. As a first step in continuum finite element analyses, the OTS was assumed to be linearly elastic and isotropic. Adhesive interactions were also accounted for via a cohesive zone model. However, the assumption of linearity gave rise to force profiles that did not match the measurements. Molecular dynamics simulations were therefore employed in order to provide further insight into the behavior of OTS. These simulations indicated that the OTS had a highly non-linear and nearly incompressible response. Based on these results, a hypo-elastic material model was developed as a convenient continuum representation of the mechanical behavior of OTS. This was then used in finite element analyses, which were able to fully reproduce the IFM force profiles. As a result, molecular and microscopic scales were linked in a relatively simple but very effective manner. This suggests that there is a class of problems where the continuum representation of the material behavior may be directly obtained from molecular analyses.