In preparation for studying the hydrolytic degradation of Estane (R) 5703 in the plastic-bonded explosive PBX 9501, the sorption (solubility) and diffusion of water in PBX 9501 and each of its components are studied experimentally and modeled theoretically. Experiments are reported that measure the weight gain or loss due to a change in the relative humidity (RH). For all of the components, the equilibrium amount of water sorbed per gram of sample is linear in the RH at low relative humidities but curves upwards at higher relative humidities. This behavior is modeled with a water cluster model. Diffusion coefficients are determined by modeling the time dependence of the water concentrations assuming Fickian diffusion, and that fits the data for some of the materials. However, all the samples that contain the explosive HMX show much more complicated behavior at high relative humidities, and that is presented and discussed. (c) 2007 Wiley Periodicals, Inc.

Recent progress in the development of a theoretical method to describe atom-diatom collisions at cold and ultra-cold temperatures is reported. Calculations are performed with hyperspherical coordinates and making use of the SVD-ERN (Smooth Variable Discretization-Enhanced Renormalized Numerov) algorithm of Colavecchia et al.(1). The advantages and disadvantages of the method are analyzed and further ways of improving the calculation are discussed.

Symmetry-induced isotope effects in recombination and collision-induced dissociation reactions are discussed. Progress on understanding the anomalous isotope effects in ozone is reviewed. Then, calculations are performed for the simpler reaction xNe+yNe+H<-->xNeyNe+H, where x and y label either identical or different isotopes. The atomic masses in the model are chosen so that symmetry is the only difference between the systems. Starting from a single potential energy surface, the properties of the bound, quasibound, and continuum states of the neon dimer are calculated. Then, the vibration rotation infinite order sudden approximation is used to calculate cross sections for all possible inelastic and dissociative processes. A rate constant matrix that exactly satisfies detailed balance is constructed. It allows recombination to occur both via direct three-body collisions and via tunneling into the quasibound states of the energy transfer mechanism. The eigenvalue rate coefficients are determined. Significant isotope effects are clearly found, and their behavior depends on the pressure, temperature, and mechanism of the reaction. Both spin statistics and symmetry breaking produce isotope effects. Under most conditions the breaking of symmetry enhances the rates, but a wide spectrum of effects is observed; they range from isotope effects with a normal mass dependence to huge, mass-independent isotope effects to cancellation and even to reversal of the isotope effects. This is the first calculation of symmetry-induced isotope effects in recombination rates from first principles. The relevance of the present effects to ozone recombination is discussed.

A clear explanation for an anomalous isotope effect in ozone formation is given in terms of the energy transfer mechanism, where the metastable states of ozone are formed first, and then stabilized by collisions with other atoms. Unusual nonstatistical properties of metastable states spectra discovered earlier [J. Chem. Phys. 118, 6298 (2003)] are incorporated into the kinetics model, where different metastable states are treated as different species, and the stabilization step is treated approximately. The population of the ozone metastable states builds up and decays through three possible O2+O channels. When different isotopes of oxygen are involved the three channels become open at different energies because of the differences in the quantum zero-point-energies (ΔZPE) of the different O2 molecules. The spectrum of metastable states is anomalously dense below the ΔZPE threshold and these states are accessible only from the lower entrance channel. Also, these low-lying metastable states are stabilized very efficiently (by collisions with third body) because they are energetically close to the bound O3 states. Such processes significantly enhance the formation rates of ozone isotopologues through the lower channels over the formation rates through the upper channels. Numerical results obtained for J=0 give isotope effects in the right direction and of the right order of magnitude. Consideration of J>0 should improve the comparison with experiment.

A global potential energy surface (PES) for the 1 4A′ spin-aligned state of Li3 is presented. The surface is constructed as a many body expansion of the potential which is the sum of pairwise additive two-body potentials plus a three-body term. The two-body potential is that for the a 3Σu+ state of the lithium dimer. It combines the most recent Rydberg–Klein–Rees potential available [A. Ross (private communication)] with well-known short and long range expansions and accurately reproduces all known experimental data. To obtain the three-body contributions, an ab initio PES was computed at 1122 points using full configuration interaction for the three valence electrons with an augmented Gaussian basis and the effective core potentials of Stevens, Basch, and Krauss [W. J. Stevens et al., J. Chem. Phys. 81, 6026 (1984)] for the other electrons. The two-body interactions are also calculated using the same basis and then subtracted from the full interaction to give the three-body term. To construct the three-body potential at arbitrary configurations we use interpolation for small perimeters of the triangle formed by the triatomic system and an analytic fitting function for large perimeters. A switching function guarantees the smoothness of the potential function everywhere. The equilibrium position occurs at D3h symmetry with a bond distance of 5.861a0, nearly 2a0 smaller than the equilibrium value of 7.886a0 of the lithium dimer. The well depth at the equilibrium is 4112.64 cm−1. This is considerably deeper than the well depth of 1001.22 cm−1 for the pairwise additive potential at its equilibrium. Three-body effects are even more important for Li3 than in the recently reported Na3 case [J. Higgins et al., J. Chem. Phys. 112, 5751 (2000)], and the nonadditive three-body term cannot be neglected in any calculation on this system.

We introduce a novel solution of the coupled-channel Schrödinger equation. This new procedure dramatically improves on our previous paper on this subject. The method uses a truly adiabatic internal basis and combines a smooth variable discretization (SVD) with an enhanced renormalized Numerov (ERN) propagator. Although the basis is truly adiabatic, this method does not require derivative coupling terms, and it involves less numerical work than previous SVD approaches. Boundary conditions are applied using Jacobi coordinates for bound states and using hyperspherical coordinates for continuum states; that allows application of the boundary conditions at smaller distances. We apply this new algorithm to the model collision-induced dissociation process Ne2+H→Ne+Ne+H for zero total angular momentum. We study the convergence of the probabilities as a function of the number of channels, distance propagated, and step size in the propagation. The method is fast, reliable, and provides considerable savings over previous propagators.

A new potential energy surface for ozone is developed. It is based on high level ab initio data and includes an accurate description of the barrier region. Full quantum reactive scattering calculations using a coupled channel approach and hyperspherical coordinates are performed on this surface for various isotopic compositions of ozone. Collision lifetimes are obtained over a wide energy range, which gives the spectrum of rovibrational metastable states (scattering resonances). This spectrum is discovered to be very nonstatistical. The spectrum of resonances is dense below the isotopic zero-point-energy threshold and sparse above it. This feature is explained by the opening of additional dissociation channels at higher energies. This behavior is a general quantum mechanical effect that should occur in other triatomic molecules.

Hydrolytic degradation data from a wide variety of experiments on Estane 5703, a commercial poly(ester urethane), are modeled with an A(AC)2 mechanism of reversible esterification and hydrolysis together with a cluster model for water concentration. The experimental conditions spanned a range of temperatures from 21 to 95degreesC, relative humidities from 0 to 100%, times up to more than 30 years, and different initial molecular weights and acidities. In addition, the experiments were performed in several different laboratories with a number of different instruments and techniques. All the experimental data, both for molecular weight and acidity, are modeled with a single set of concentration-independent rate coefficients, and the kinetic model fits the data well and constitutes a robust model of the hydrolytic degradation of this polymer. The results also show that ester hydrolysis is the dominant cause of the molecular weight loss of Estane 5703 in indoor storage at ambient temperatures and humidities. (C) 2003 Wiley Periodicals, Inc.

In preparation for studying the kinetics of the hydrolysis of Estane® 5703, published hydrolysis data for a similar poly(butylene adipate) (herein called 63 PBA) have been modeled. Poly(ester urethanes) are known to degrade by acid-catalyzed hydrolysis of the ester links, and the data on 63 PBA show that this degradation is reversible at low relative humidities (RHs). Previous work with these data was unable to fit them with concentration-independent rate coefficients. It is shown herein that, with the water-concentration model of the preceding article and the AAC2 mechanism of reversible hydrolysis/esterification, the experimental kinetic data that vary across temperature, RH, and starting molecular weight can be fit with a single set of concentration-independent rate coefficients. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 192–200, 2002

In preparation for studying the hydrolytic degradation of Estane® 5703 and related poly(ester urethane) elastomers, the absorption (solubility) and diffusion of water in these polymers have been examined experimentally and modeled theoretically. Weight gain and loss experiments have been carried out. The amount of water absorbed per gram of sample was linear at low relative humidities (RHs) but curved upward at higher RHs. This curvature was not fit by Henry's law or the Flory–Huggins equation but was easily fit by a water-cluster model. Diffusion coefficients were determined by fitting the time dependence of the sample weights, and the diffusion appeared Fickian to within experimental uncertainty. The similarity of related polymers was used to determine the approximate temperature dependence of the absorption. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 181–191, 2002

Symmetry constraints are built into a semiclassical propagation scheme. It is then applied to treat H+Ne2 collisions at 30 K, where quantum selection rules restrict the final rotational states of symmetric Ne2 molecules to the even manifold. The cross sections for state-to-state transitions are calculated for symmetric and nonsymmetric isotopic compositions of Ne2. All bound and long-lived quasibound (trapped behind the centrifugal barrier) states of Ne2 are considered. This semiclassical method captures symmetry effects and shows satisfactory agreement with the quantum results.

The barrier associated with the dissociation and recombination of ozone has been calculated using highly correlated ab initio methods. Our calculations show that, for fixed equilibrium values of the bending angle and one bond distance, there is a very small barrier, 100cm−1, as opposed to much larger values previously reported. When the saddle point geometry is optimized, the reaction path still contains a barrier but the top of the barrier lies below the dissociation limit.

The exact quantum theory of atomic recombination and collision-induced dissociation (CID) is presented using hyperspherical coordinates. Delves’ coordinates are emphasized, methods for doing numerically exact calculations are discussed and implemented, and fully converged dissociation probabilities (J=0) are presented for a model H+Ne2⇌H+Ne+Ne system. These are the first accurate CID calculations reported for any atomic system in the full three-dimensional physical space.

A programming error, which affects many of the numbers, tables, and figures of this paper, is corrected. It does not affect any of the conclusions of the work.

A new hybrid numerical technique which utilizes both the DVR (Discrete Variable Representation) and FBR (Finite Basis Representation) to solve for the full 5D surface functions in the three-atom problem in hyperspherical coordinates for nonzero total angular momentum (J≠0) is reported. This method accurately treats the Eckart singularities in the kinetic energy operator which occur at both the north pole and equator of the 2D hypersphere in body-frame coordinates. The effects of the Eckart singularities on the surface function energies for HD2 are investigated and it is shown that an accurate treatment of these singularities is crucial in order to obtain the correct results. An improper treatment of the Eckart singularities could be a source for some of the discrepancies between recent experimental results and theory for the reaction H+D2→HD+D.