Analytical solutions for diffusion-controlled adsorption kinetics with non-linear adsorption isotherms

A regular perturbation series method provides a solution to the diffusion equation when the boundary condition is a non-linear adsorption isotherm. For adsorption at the interface the Freundlich and Langmuir isotherms yield power series in the square root of time. Convergence of the power series solutions is improved by applying the Shanks transformation. The solutions are compared to limiting cases and to published numerical solutions. The results are most accurate for small time where the numerical finite difference method is least reliable.     

Combined experimental/theoretical investigation of the He+ICl interactions. I. Rovibronic spectrum of He...ICl complexes in the ICl B-X, 3-0 region

Transitions of two different stereoisomers of the He...ICl(X,v" = 0) weakly bound complex, one with a T-shaped orientation and another that is most likely linear, have been observed in laser-induced fluorescence experiments performed in the ICl B-X region. Here we present experimental and theoretical results aimed at confirming the previous assignments and at gaining additional insights into the He+ICl interactions. High resolution action spectra were recorded in the same region to identify those features that could be attributed to transitions of the He...I35Cl(X,v" = 0) isomers and not to higher-order complexes, Hen...I35Cl, where n > or = 2, or I37Cl containing species. Calculations of the rovibronic spectra of the He...I35Cl complexes in the ICl B-X, 2-0 and 3-0 regions were performed using an ab initio potential energy surface for the He+ICl(X,v" = 0) ground state and two different pairwise additive potentials for the He+ICl(B,v' = 2,3) excited states. The rotation-vibration energies and wave functions for the He cdots, three dots, centered I35Cl complexes were obtained for all bound states with total angular momentum J < 10 using both of these potentials. Electronic spectra were generated using these results, assuming that the transition moment lies along the ICl bond and is not perturbed by the presence of the helium atom. The calculations qualitatively reproduce the He cdots, three dots, centered I35Cl action spectrum and strongly support the previous assignments. The calculations also indicate that some of the spectral congestion observed near the linear band may be attributed to transitions of the linear isomer to multiple intermolecular levels in the excited state. Coriolis coupling strongly mixes He cdots, three dots, centered ICl(B,v') states with rotational excitation, making simulations and assignments of the linear band observed in the experimental spectrum difficult.     

Argon predissociation spectroscopy of the OH-.H2O and Cl-.H2O complexes in the 1000-1900 cm(-1) region: intramolecular bending transitions and the search for the shared-proton fundamental in the hydroxide monohydrate

We present argon predissociation vibrational spectra of the OH(-).H(2)O and Cl(-).H(2)O complexes in the 1000-1900 cm(-1) energy range, far below the OH stretching region reported in previous studies. This extension allows us to explore the fundamental transitions of the intramolecular bending vibrations associated with the water molecule, as well as that of the shared proton inferred from previous assignments of overtones in the higher energy region. Although the water bending fundamental in the Cl(-).H(2)O spectrum is in very good agreement with expectations, the OH(-).H(2)O spectrum is quite different than anticipated, being dominated by a strong feature at 1090 cm(-1). New full-dimensionality calculations of the OH(-).H(2)O vibrational level structure using diffusion Monte Carlo and the VSCF/CI methods indicate this band arises from excitation of the shared proton.     

The colloidal force of bead-spring chains in a good solvent

A recently developed density functional theory (DFT) for tethered bead-spring chains is used to investigate colloidal forces for the good solvent case. A planar surface of tethered chains is opposed to a bare, hard wall and the force exerted on the bare wall is calculated by way of the contact density. Previously, the case of large wall separation was investigated. The density profiles of the unperturbed chains, in that case, were found to be neither stepfunctions nor parabolas and were shown to accurately predict computer simulation results. In the present paper, the surface forces that result from the distortion of these density profiles at finite wall separation is studied. The resulting force function is analyzed for varying surface coverages, wall separations, and chain lengths. The results are found to be in near quantitative agreement with the scaling predictions of Alexander [S. Alexander, J. Phys. (Paris) 38, 983 (1977)] when the layer thickness is "correctly" defined. Finally, a hybrid Alexander-DFT theory is suggested for the analysis of experimental results.     

Transition state dynamics of Ar(n).(IHI) (n = 0-20)

Classical trajectory simulations of the dynamics of Ar(n).(IHI) with n = 0-20 are performed to investigate the effects of solvation on the transition state dynamics of the I + HI reaction. Initial conditions for the classical trajectories are sampled from the quantum ground-state phase space distribution for Ar(n).(IHI)-, given by the Wigner distribution function. Neumark and co-workers recently reported a shift of the Ar(n).(IHI)- photoelectron spectra to lower electron kinetic energies when the number of argon atoms was increased from 0 to 15. Analogous shifts are found in the present calculations, and excellent agreement between the experimental and calculated shifts is found. Longer lifetimes of the IHI complex and increasing energy transfer between the hydrogen atom and the argon and iodine atoms are also observed as the number of argon atoms is increased.     

A unified view of bulk property theories for stochastic and periodic media

The response of a continuum characterized by two widely differing length scales, parameterized by the dimensionless ratio, is considered in the context of the composite materials problem. The development of a bulk property theory appropriate in the 0 limit is examined both from the perspective of the deterministic homogenization literature and the smoothing method associated with statistical continuum theory and a unified framework established. The extension of bulk property theories through the development of ordered expansions in powers of is discussed and specifically related to analogous treatments in linear-gas relaxation theory. Finally, the projection operator techniques of homogenization and smoothing are compared to a proper two-scale perturbation analysis.

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Résumé Les propriétés d'un continu caractérisé par 2 échelles de longueur très différente parametrisées par leur rapport non dimensionnel sont décrites dans le contexte concernant le problème des matières composées.Le développement d'une théorie des proprietés de volume valable dans la limite 0 est examiné de 2 points de vue: la littérature sur l'homogénisation déterministique et la méthode de lissage liée à la théorie statistique du continu. Sur cette base on établit une théorie unifié. L'extension des théories de propriétés de volume par le devéloppement d'expansions ordonnées en puissances de est discutée et spécifiquement mise en relation avec des procédées analogues dans la théorie de relaxation linéaire des gaz.Enfin les techniques des opérateurs de projection, d'homogénisation et de lissage sont comparées à une analyse appropriée de perturbation à 2 échelles.

     

Full-dimensional vibrational calculations for H5O2+ using an ab initio potential energy surface

We report quantum diffusion Monte Carlo (DMC) and variational calculations in full dimensionality for selected vibrational states of H(5)O(2) (+) using a new ab initio potential energy surface [X. Huang, B. Braams, and J. M. Bowman, J. Chem. Phys. 122, 044308 (2005)]. The energy and properties of the zero-point state are focused on in the rigorous DMC calculations. OH-stretch fundamentals are also calculated using "fixed-node" DMC calculations and variationally using two versions of the code MULTIMODE. These results are compared with infrared multiphoton dissociation measurements of Yeh et al. [L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys. 91, 7319 (1989)]. Some preliminary results for the energies of several modes of the shared hydrogen are also reported.     

Femtosecond dynamics of Cu(H(2)O)(2)

The ultrafast relaxation dynamics of Cu(H(2)O)(2) is investigated using femtosecond photodetachment-photoionization spectroscopy. In addition, stationary points on the Cu(H(2)O)(2) anion, neutral, and cation potential energy surfaces are characterized by ab initio electronic structure calculations. Electron photodetachment from Cu(-)(H(2)O)(2) initiates the dynamics on the ground-state potential energy surface of neutral Cu(H(2)O)(2). The resulting Cu(H(2)O)(2) complexes experience large-amplitude H(2)O reorientation and dissociation. The time evolution of the Cu(H(2)O)(2) fragmentation products is monitored by time-resolved resonant multiphoton ionization. The parent ion, Cu(+)(H(2)O)(2), is not detected above background levels. The rise to a maximum of the Cu(+) signal from Cu(-)(H(2)O)(2), and the decay of the Cu(+)(H(2)O) signal from Cu(-)(H(2)O)(2) have similar tau approximately 10 ps time dependences to the corresponding signals from Cu(-)(H(2)O), but display clear differences at very short and long times. The experimental observations can be understood in terms of the following picture. Prompt dissociation of H(2)O from nascent Cu(H(2)O)(2) gives rise to a vibrationally excited Cu(H(2)O) complex, which dissociates to Cu+H(2)O due to coupling of H(2)O internal rotation to the dissociation coordinate. This prompt dissociation removes all intra-H(2)O vibrational excitation from the intermediate Cu(H(2)O) fragment, which quenches the long time vibrational predissociation to Cu+H(2)O previously observed in analogous experiments on Cu(-)(H(2)O).     

Structures of protein-protein complexes are docked using only NMR restraints from residual dipolar coupling and chemical shift perturbations

NMR structures of protein-protein and protein-ligand complexes rely heavily on intermolecular NOEs. Recent work has shown that if no significant conformational changes occur upon complex formation residual dipolar coupling can replace most of the NOE restraints in protein-protein complexes, while restraints derived from chemical shift perturbations can largely replace intermolecular NOEs in protein-ligand structures. By combining restraints from chemical shift perturbations with orientation restraints derived from measurements of residual dipolar couplings, we show that the structure of the EIN-HPr complex can be calculated without NOE restraints. The final structure, built from the crystal structures of EIN and HPr in their uncomplexed form and docked only with NMR restraints, places HPr within 2.5 A of the position determined from the mean NMR structure of the complex.