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Notes: By time-of-flight techniques, electron mobilities have been measured in vapor deposited films of the title compound. The results were compared to predictions of the disorder formalism, due to Bässler and co-workers, and models based on polaron formation. The results lead to the conclusion that fluctuations in hopping site energies are the major contribution to the activation energy. For consistency between experiment and predictions of the formalism, however, an additional source of activation is required. The source of this activation is believed due to either polaron formation or trapping. The width of the hopping site manifold, σ, is determined as 0.080 eV and the positional disorder parameter, Σ, as 1.0. The interpretation of these results by a model in which transport occurs only by polaron displacement leads to inconsistencies with both the temperature and field dependencies of the mobility.

Notes: In this work, we test a hypothesized form for the stationary solution Ps(X,Y) of the stochastic master equation for a reacting chemical system with two reactive intermediates X and Y, and multiple steady states. Thermodynamic analyses and the exact results for nonautocatalytic or equilibrating systems suggest an approximation of the form Pas(X,Y)=N exp(−φ/kT), where the function φ is a line integral of a differential "excess'' work Fφ, which depends on species-specific affinities. The differential Fφ is inexact. In a preceding paper, we have given an analytic argument for the use of the deterministic kinetic trajectory, connecting (X,Y) to the steady state (Xs,Ys) as the path of integration for Fφ. Here, we show that use of the deterministic trajectories leads to a potential φdet which is continuous across the separatrix between the domains of attraction of the two stable steady states in the model studied.We compare the approximate form of Ps(X,Y) thus generated with numerical solutions of the time-dependent master equation in the limit of attainment of a stationary distribution. Because the time required for convergence to the stationary distribution scales as eN with the particle number N in cases with two stable steady states, the numerical work is limited to systems with O(10–100) X and Y particles. System size affects the accuracy of the approximation. To isolate system-size effects, we compare numerical solutions and the corresponding approximations to Ps(X) for two single-intermediate master equations, since the approximation becomes exact in the limit of large particle number for such equations. Based on these comparisons, for the systems with two intermediates, the agreement between the approximation and the numerical solutions is reasonable. The agreement improves as the number of particles increases in those test cases where it has thus far been possible to vary the system size over an order of magnitude. The results obtained by integrating along deterministic trajectories are better than those from straight-line or line-segment paths. The numerical work on small, single-variable systems with two stable steady states leads to two new observations: (i) the relative heights of the steady state peaks in the exact stationary distribution may invert as the system size increases and (ii) an approximation used commonly for particle counting may give results inconsistent with the exact stationary distribution when the particle number is small, while an alternative approximation improves the agreement.

Notes: We continue our development of a global thermodynamic and stochastic theory of open chemical systems far from equilibrium with an analysis of a broad class of isothermal, multicomponent reaction mechanisms with multiple steady states, studied under the assumption of local equilibrium. We generalize species-specific affinities of reaction intermediates, obtained in prior work for nonautocatalytic reaction mechanisms, to autocatalytic kinetics and define with these affinities an excess free energy differential Fφ. The quantity Fφ is the difference between the work required to reverse a spontaneous concentration change and the work available when the same concentration change is imposed on a system in a reference steady state. The integral of Fφ is in general not a state function; in contrast, the function φdet obtained by integrating Fφ along deterministic kinetic trajectories is a state function, as well as an identifiable term in the time-integrated dissipation. Unlike the total integrated dissipation, φdet remains finite during the infinite duration of the system's relaxation to a steady state and hence φdet can be used to characterize that process. The variational relation δφ≥0 is shown to be a necessary and sufficient thermodynamic criterion for a stable steady state in terms of the excess work of displacement of the intermediates and φdet is a Liapunov function in the domain of attraction of such steady states. Based on these results and earlier work with nonautocatalytic and equilibrating systems, we hypothesize that the stationary distribution of the master equation may be obtained in the form Ps=N exp(−φdet/kT) and provide an analytical argument for this form for macroscopic systems. This generalizes the Einstein fluctuation formula to multivariable systems with multiple steady states, far from equilibrium. In the following article, the utility of the approximation to Ps for systems with single or multiple intermediates, and single or multiple steady states is shown by comparison with numerical solutions of the master equation.

Notes: The relaxation dynamics of a polymer chain strongly adsorbed to a solid surface are simulated via a kinetic Ising model that includes chain connectivity constraints (steric hindrance, rotational strain, and configurational entropy). The two polymer architectures examined consist of one or two chemisorbing functional groups per segment. In both architectures, the chemisorbed polymer chain is trapped in nonequilibrium conformational states at low temperatures, but relaxes to equilibrium at higher temperatures with stretched exponential (KWW) relaxation kinetics. The average relaxation time for the two pendant group architecture has a strongly non-Arrhenius temperature dependence that obeys the Vogel–Fulcher law. In contrast, average relaxation times for the one pendant group architecture cannot be described by the Vogel–Fulcher law.

Notes: An experimental system composed of a standard negative ion source and an Nd:YAG laser is used to study the formation of negative ions by laser impact and the interaction of the laser with the negative ion beam. Using a Q-switched Nd:YAG laser (about 107 W/cm2) impinging on the solid FeS sample of a Cs-sputter source, pulses of negative ions of sulphur with a peak intensity of 3 mA and a width of 150 ns were observed. The time structure of the pulses is measured and shows a complex behavior, not yet fully understood. The same experimental system is used to analyze the production of rare negative ions in the lanthanide and actinide regions and to study their interaction with a laser beam. Cross sections for photodetachment in La− and Th− are measured.