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The results of our earlier work [C. Brooksby, O. V. Prezhdo, and P. J. Reid, J. Chem. Phys. 119, 9111 (2003)] rationalizing the surprisingly weak solvent dependence of the dynamics following photoexcitation of chlorine dioxide in water, chloroform, and cyclohexane are thoroughly tested. Comparisons are made between equilibrium and nonequilibrium solvent response, equilibrium response in the ground and excited electronic states, as well as the cumulant and direct evaluation of the optical response function. In general, the linear response and cumulant approximations are found to hold, although minor deviations are found with all solvents. The ground state, linear response, and cumulant data show best agreement with experiment, most likely due to the better tested ground-state force field and the robust behavior of the linear response and cumulant approximations. The main conclusion of our earlier work explaining the weak solvent dependence by the domination of the van der Waals interaction component remains intact within the more advanced treatments. However, the molecular origin of this surprising experimental observation is different in water and chloroform compared to cyclohexane. [ABSTRACT FROM AUTHOR]

The solvation dynamics following photoexcitation of chlorine dioxide (OClO) in different solvents are investigated by classical molecular dynamics. Following previous work on the aqueous response to OClO photoexcitation [J. Chem. Phys. 118, 4563 (2003)], the present study considers the response of chloroform and cyclohexane; these three liquids present unique solvent environments that differ significantly in both polarity and structure. The study is designed to ascertain the origin of the solvent-invariant homogeneous linewidth associated with OClO photoexcitation and to confirm, at the molecular level, whether the relaxation dynamics are similar across dissimilar solvents due to chance or a common relaxation origin. The results obtained here are used to predict the time scale of solvent-induced optical dephasing, and excellent agreement with experiment is observed for all solvents. Analysis demonstrates that the solvation dynamics of OClO are dominated by short-ranged mechanical solute–solvent interactions regardless of the identity and electrostatic properties of the solvent. Low-frequency translational motions dominate the coupling spectrum, and virtually no contribution to energy gap relaxation is achieved through intramolecular solvent motions. The invariant homogeneous linewidth is attributed to the similarity in the primary response of all solvents to OClO photoexcitation. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The solvation dynamics following photoexcitation of aqueous chlorine dioxide (OClO) are investigated by classical molecular dynamics. A total of four OClO/water models are employed, including standard and customized OClO models together with SPC/F and TIP3P water. The simulation results are used to predict the time scale of solvent-induced optical dephasing, and excellent agreement with experiment is observed. The simulations demonstrate that the solvation dynamics of aqueous OClO are dominated by the short-ranged mechanical solute-solvent interactions. When compared to the aqueous solvation of spherical solutes, the solvation dynamics of OClO exhibit a novel effect. The role of the faster translational and librational water motions is suppressed in the dielectric component of the response, but is emphasized in the mechanical response, in stark contrast to the results for other spherical systems. The faster translational motions appear in the mechanical response due to the noncentrosymmetric nature of the OclO-water interaction, enhanced by OclO-water hydrogen bonding. [ABSTRACT FROM AUTHOR]

The quantum interference pattern in the double-slit experiment is qualitatively reproduced by independent classical trajectories evolving on an effective potential obtained in the lowest order quantized Hamilton dynamics approach. The quantum effects appear due to a simple modification of the original classical potential that is sufficient to obtain a diffraction maximum in the middle between the two slits and an auxiliary diffraction structure on the sides of the central maximum. [Copyright &y& Elsevier]

Three novel approaches extending quantum-classical non-adiabatic (NA) molecular dynamics (MD) to include quantum effects of solvent environments are described. In a standard NA-MD the solute subsystem is treated quantum mechanically, while the larger solvent part of a system is treated classically. The three novel approaches presented here are based on the Bohmian formulation of quantum mechanics, the stochastic Schro¨dinger equation for the evolution of open quantum systems and the quantized Hamilton dynamics generalization of classical mechanics. The approaches extend the standard NA-MD to incorporate the following quantum effects of the solvent. (1) Branching, i.e. the ability of solvent quantum wave packets to split and follow asymptotically diverging trajectories correlated with different quantum states of the solute. (2) Decoherence, i.e. loss of quantum interference within the solute subsystem induced by the diverging solvent trajectories. (3) Zero point energy that contributes to NA coupling and must be preserved during the energy exchange between solvent and solute degrees of freedom. The Bohmian quantum-classical mechanics, stochastic mean-field and quantized mean-field approximations incorporate the quantum solvent effects into the standard quantum-classical NA-MD in a straightforward and efficient way that can be easily applied to quantum dynamics of condensed phase chemical systems. [Copyright &y& Elsevier]

Summary: To determine whether survival outcomes of younger patients with oral cavity squamous cell cancer (OSCC) differs from older patients in the US. A retrospective cohort study using data from the Surveillance, Epidemiology and End Results (SEER) registry. We studied cases (n =19681) of OSCC diagnosed from 1973 to 1999 and used age cutoffs at 40, 45, 50, and 55years. Control groups of older patients were retrospectively matched on gender, race, cancer subsite, and stage of disease. Survival was estimated using the Kaplan–Meier method. A propensity score matching produced groups with similar distributions of patient and disease characteristics. Between these matched groups, younger patients had a significantly better five-year survival (age 40: 63.4% vs. 80.6%, p <0.0001; age 45: 59.0% vs. 72.8%, p <0.0001; age 50: 55.5% vs. 67.2%, p <0.0001; age 55: 54.0% vs. 64.3%, p <0.0001). These results confirm recent results using population-based data that suggest better overall survival in younger patients. [Copyright &y& Elsevier]