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As shown by W. H. Miller in a seminal article [J. Chem. Phys. 53, 3578 (1970)], the most convenient and accurate semiclassical (SC) theory of molecular scattering in action-angle coordinates is based on the initial value representation (IVR) and the use of shifted angles, which are different from the natural angles usually used in the quantum and classical treatments. Here, we show for an inelastic molecular collision that the initial and final shifted angles define three-segment classical paths that are exactly those involved in the classical-limit of Tannor–Weeks quantum scattering theory [J. Chem. Phys. 98, 3884 (1993)], provided that the translational wave packets |g+⟩ and |g−⟩ into play in this theory are both taken at |0⟩. Assuming this to be the case, using van Vleck propagators, and applying the stationary phase approximation, Miller's SCIVR expression of S-matrix elements is found, with an additional cut-off factor canceling the energetically forbidden transition probabilities. This factor, however, is close to unity in most practical cases. Furthermore, these developments show that the Møller operators underlie Miller's formulation, thus confirming, for molecular collisions, the results recently established in the simpler case of light-induced rotational transitions [L. Bonnet, J. Chem. Phys. 153, 174102 (2020)]. Last but not least, we show, based on the previous results, that for processes involving long-range anisotropic forces, implementing the Skinner–Miller method [Chem. Phys. Lett. 300, 20 (1999)] in shifted coordinates makes its predictions both easier and more accurate than in natural coordinates. [ABSTRACT FROM AUTHOR]

In the semiclassical theory of rotational transitions, S-matrix elements are expressed as integrals over initial and final angles of probability amplitudes calculated along the classical paths joining these angles, before final passage to an initial value representation [W. H. Miller, J. Phys. Chem. A 105, 2942 (2001)]. These angles can be either natural angles fixing the orientation of the rotor or angles shifted with respect to the previous ones so as to vary only within the interaction region causing the transitions. The two approaches, however, were recently shown to lead to different predictions. While the theory in natural angles lacks precision and exhibits unphysical behavior, the theory in shifted angles is much more accurate and physically well behaved [L. Bonnet, J. Chem. Phys. 153, 174102 (2020)]. The present work is devoted to the analysis of this unexpected finding. [ABSTRACT FROM AUTHOR]

The initial value representation (IVR) was proposed five decades ago by Miller [J. Chem. Phys. 53, 3578 (1970)] in order to improve the feasibility and accuracy of semiclassical (SC) scattering calculations. Møller operators, which play a fundamental role in quantum scattering theory, do not appear in his formulation based on action-angle coordinates. These operators were introduced much later by Garashchuk and Light [J. Chem. Phys. 114, 1060 (2001)] in SC-IVR calculations performed in Cartesian coordinates within the Tannor and Weeks [J. Chem. Phys. 98, 3884 (1993)] formulation of quantum scattering theory. Remarkably, Møller operators were found to boost the numerical efficiency of SC-IVR calculations. The purpose of this work is to show within a simple model of light-induced rotational transitions that, in fact, Møller operators were already underlying Miller's pioneering formulation. In line with the results of Garashchuk and Light [J. Chem. Phys. 114, 1060 (2001)], removing the action of these operators in Miller's theory strongly decreases its numerical efficiency. [ABSTRACT FROM AUTHOR]

We argue that statistical theories are generally unable to accurately predict state-resolved differential cross sections for triatomic bimolecular reactions studied in beam experiments, even in the idealized limit where the dynamics are fully chaotic. The basic reason is that quenching of interferences between partial waves is less efficient than intuitively expected, especially around the poles. [ABSTRACT FROM AUTHOR]

The dynamics of the N(2D) + H2(v = 0, j = 0) reaction has been theoretically studied between 200 and 300 K by combining the classical trajectory method and the WKB penetration factor through the early barrier involved in this reaction. The resulting opacity functions, cross sections and rate constants are in reasonable agreement with accurate quantum wave packet results [S. Lin and H. Guo, J. Chem. Phys. 124, 031,101 (2006)] and experimental measurements [T. Suzuki et al., J. Chem. Soc., Faraday Trans, 1993, 89, 995]. Nevertheless, our treatment tends to underestimate the importance of deep tunneling, probably due to the crude linear approximation of tunneling paths employed in our study. [ABSTRACT FROM AUTHOR]

Traditional statistical approaches, entirely based on transition state theory (TST), do not allow the description of rotational state distributions in the products of indirect reactions governed by short-range forces. Owing to the interpretative power of TST, this limitation has long been acting as a brake upon a deep understanding of determining attributes of indirect reaction dynamics. Recently, however, we developed a statisticodynamical approach (SDA) of final state distributions for triatomic unimolecular reactions [P. Larrégaray, L. Bonnet, and J. C. Rayez, J. Chem. Phys. 114, 3349 (2001); Phys. Chem. Chem. Phys. 4, 1577 (2002); 4, 1781 (2002)]. The approach combines TST for the description of state distributions at the transition state (TS) and the linear transformation model for the description of their alteration on the way from the TS to the products. The whole description is mostly analytical, thus keeping the rationalizing spirit of TST. The goal of the present series is to extend SDA to the case of four-atom planar unimolecular reactions, assuming that internal vibrations of the nascent products are conserved from the TS on. This first part is concerned with formal developments while the remaining parts deal with their validation and application, in particular to the fragmentation of isocyanic acid. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In the first part of this series, we proposed a statisticodynamical approach of state distributions in the products of four-atom planar unimolecular reactions governed by short-range forces. In this second part, the approach is tested against quasiclassical trajectory calculations on an ab initio potential energy surface. The process considered is the fragmentation of isocyanic acid in the first excited singlet electronic state. The study leads to a very good agreement between both methods. In addition to that, we pinpoint in the barrier case the main mechanical parameters governing the shape of rotational state distributions. It appears that these parameters are related to two distinct physical effects. The first one is of the impulsive type. The second, already observed in triatomic processes, is the so-called bending effect. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Three series of novel food contact approved and low-toxic coatings for glass toughening applications were successfully prepared based on dicyandiamide and biobased epoxy compounds, e.g. epoxidized cardanol (NC514), diglycidyl ether of vanillin (DGEVA), triglycidyl ether of phloroglucinol (TGEP). Processability of formulations in bulk and in aqueous phase, and optimum materials were carefully investigated. The cure temperature of these epoxide:amine systems ranged from 160 to 250 °C, for which TGEP showed the highest reactivity. The developed materials exhibited excellent thermal stability and a wide range of glass transition temperature (Tg) was achieved, from 29 to 187 °C. The glass adhesion and mechanical properties were characterized by adhesion test and by mechanical ring test, respectively. The results revealed excellent glass adhesion properties without adhesion promotor addition and enhanced glass mechanical properties with all materials. These food contact and lowly-toxic materials are promising alternatives for DGEBA-based materials in widespread applications. [ABSTRACT FROM AUTHOR]

The F + CHD3(v) reaction is a benchmark system in polyatomic reactions. Theoretical/experimental comparisons have been reported in recent years that present some controversies, specifically the role of the reactant CH stretching vibrational excitation, CHD3(ν1 = 1), on the reactivity of both isotope channels, DF(v) + CHD2(v') and HF(v) + CD3(v'). However, in many cases, these comparisons are not made on an equal footing. Previous theoretical studies were concerned with overall reactivity of each isotope channel, while fine velocity map imaging experiments provided results in a product pair-correlated manner. In order to shed some light on these controversies, we perform here a pair-correlated theory/experiment comparison for the title reaction, using quasi-classical trajectory calculations on a full dimensional potential energy surface. When these calculations are analyzed in a quantum spirit, i.e., by discarding those trajectories whose results do not meet quantum-mechanical requirements and aiming to reproduce stringent experimental constraints, some of the discrepancies on overall reactivity and the effect of the CH vibrational excitation are now resolved. Agreement with the available experimental studies, though still qualitative in some aspects, has noticeably improved. [ABSTRACT FROM AUTHOR]

Ten years ago, Liu and co-workers measured pair-correlated speed distributions for OH+CH 4 /CD 4 reactions by means of velocity map imaging (VMI) techniques at a collision energy of ∼10 kcal/mol [B. Zhang, W. Shiu, J. J. Lin and K. Liu, J. Chem. Phys 122, 131102 (2005); B. Zhang, W. Shiu and K. Liu, J. Phys. Chem. A 109, 8989 (2005)]. Recently, two of us could semi-quantitatively reproduce these measurements by performing full-dimensional quasi-classical trajectory calculations in a quantum spirit on an ab-initio potential energy surface of their own [J. Espinosa-Garcia and J. C. Corchado, Theor. Chem. Acc. (2015) 134: 6; J. Phys. Chem. B 120, 1446 (2016)]. The goal of the present work is to show that these results can be significantly improved by adding a few more constraints in order to better comply with the restrictions imposed by VMI. Overall, the level of agreement between theory and experiment is remarkable owing to the large dimensionality of the reactions under scrutiny. This is an encouraging result considering the computational challenges of quantum scattering calculations for such large processes. [ABSTRACT FROM AUTHOR]

Molecular beam experiments provide fascinating data on how atoms move in the course of chemical reactions. In order to theoretically reproduce these data at relatively low computational cost and to interpret them, nuclei are often treated as classical particles, even though we have known for about a century that, in the range of energies usually available to chemical systems, their motion is best described by the laws of quantum mechanics. Nevertheless, over the last decade this approximation has been shown to work unexpectedly well, provided that a few constraints are introduced into the calculations in order to take into account the quantisation of product internal motions. Why this is so and the nature of the previous constraints are the central issues of this review article. [ABSTRACT FROM AUTHOR]

The angle---velocity and product vibrational state distributions for the OH + D2 reaction at a collision energy of 0.28 eV have been calculated using the quasi-classical trajectory--Gaussian binning (QCT--GB) method and the Wu--Schatz--Lendvay--Fang--Harding (WSLFH) analytical potential energy surface. Comparison with high resolution molecular beam experiments shows that, differing from what happens when using the standard QCT method (i.e., histogram binning), very good results are obtained for both distributions. Hence, the strong differences previously observed between QCT and experimental results mainly come from an inadequate pseudoquantization of HOD rather than from other quantum effects. This is probably the first time that such a high level of agreement between theory and high resolution experimental data has been found in polyatomic reaction dynamics. [ABSTRACT FROM AUTHOR]

Mastication is a complex sensory-motor activity whereby a food product is transformed into a bolus. Consumers mainly perceive the sensory properties of the food during the intra-oral manipulation of the product. Consequently, the quality of the chewing process could have consequences on the perception of sensory properties and food choice. By focusing on meat products, this study aimed to analyze the influence of dental status on (i) dynamic adaptation of the chewing behavior (evaluated by electromyography) to the changes in texture during bolus formation and (ii) bolus properties (mechanical resistance and saliva incorporation) obtained from meat of different initial textures. Two groups of subjects (dentate subjects and denture wearers), known to present highly different chewing efficiency, were compared. For both groups, salivary flow rates were evaluated at rest and after stimulation by chewing (paraffin and meat). The salivary flow rates, assessed during chewing of a nonedible matrix (paraffin), were a good predictor of salivary flow rates induced by meat chewing for both groups of subjects. Salivary flow rates were not affected by the dental status. In contrast, the chewing behavior varied between groups. For denture wearers, the chewing pattern was strongly impaired and not adapted to the changes in meat structure during bolus formation. Denture wearers swallowed less fragmented boli than dentate subjects, but boli had a similar level of moisture for both groups of subjects. [ABSTRACT FROM AUTHOR]

Classical &Smacr; matrix theory is applied to the description of microcanonical unimolecular rate constants in the chaotic scattering regime. If we postulate that the semiclassical treatment satisfyingly describes the relative values of the final populations when only a few product states are available, we arrive, for processes involving tight transition states (TSs), at the following conclusions: (a) there is no semiclassical transition state theory (TST), a result in agreement with previous findings by Pechukas and Miller; stricto sensus, the exact proportionality between the rate constant kuni(E) and the available number N‡(E) of quantum states at the TS is not founded; (b) kuni(E) should depend rather smoothly on E, even when tunneling is negligible; and (c) TST, however, provides a very satisfying quantitative description of rate constants when N‡(E) is large, which is mostly the case in practice. [Copyright &y& Elsevier]

In standard quasiclassical trajectory calculations, each trajectory has the same statistical weight. Alternately, the Gaussian weighting method is an ad hoc procedure which consists in weighting each trajectory by a Gaussian-like coefficient such that the closer the final actions to integer values, the larger the coefficient. The goal of the present note is to justify such a method in the framework of classical S matrix theory. [Copyright &y& Elsevier]

Kinematic rotations for four body processes canbe conveniently represented as arcs connecting the different reactive rearrangements, (T + UVW, TU + VW, TUV + W and all permutations). The arcs can be considered as forming great circles on a sphere, which is therefore a convenient manifold for setting up symmetric coordinates in asymptotic rearrangement channels: in the particular cases where the reactions are collinearly dominated, the sphere provides the full chart for the (fixed moment of inertia or hyperradial) mapping of the potential energy surface. Also,the representations can be extended to include connections to a formulation where two particles are symmetrically treated with respect to a third one-as introduced in the Journal of Chemical Physics (1986, 85, 1355)-and to encompass the asymptotic situation of the four body system decomposing into three fragments (T + U + VW, T + UV + W, etc...). Comments are made on other cases pertaining to the symmetric parametrizations of four centre processes. [ABSTRACT FROM AUTHOR]

We present results of a theoretical investigation on the dynamics of the C(1D)+H2 reaction and the corresponding isotopic variants in which the carbon atom collides either with D2 or HD. Statistical techniques have been tested in comparison with the recent experimental information at low temperature (T < 300 K) and exact quantum mechanical calculations reported on the title reactions in an attempt to establish their possible complex-forming character. Our study includes the calculation of probabilities, rotational distributions, integral cross sections, differential cross sections, and rate constants. Previous quantum mechanical results have been extended here to complete the analysis of the underlying mechanisms which govern the collision process. [ABSTRACT FROM AUTHOR]

In recent years, combined experimental and theoretical efforts have brought valuable information on the kinetics of reactive collisions between molecular hydrogen and an electronically excited atom X (where X = C (1 D) , N (2 D) , O (1 D) or S (1 D)). These four reactions have been comparatively studied together in numerous occasions in the past due to the similar importance of complex-forming mechanisms found in their overall dynamics. In this work, we compile the most updated information on these investigations making a special emphasis from the theoretical side on statistically based techniques, in an attempt to test the possible insertion nature of the overall dynamics. Besides a description of the experimental details of the kinetics investigation, a comparison of the measured rate constants over a temperature range between 50 and 300 K with the most recent theoretical calculations is presented. [ABSTRACT FROM AUTHOR]

The dynamics of the singlet channel of the Si+O2→SiO+O reaction is investigated by means of quasiclassical trajectory (QCT) calculations and two statistical based methods, the statistical quantum method (SQM) and a semiclassical version of phase space theory (PST). The dynamics calculations have been performed on the ground 1A′ potential energy surface of Dayou and Spielfiedel [J. Chem. Phys. 119, 4237 (2003)] for a wide range of collision energies (Ec=5–400 meV) and initial O2 rotational states (j=1–13). The overall dynamics is found to be highly sensitive to the selected initial conditions of the reaction, the increase in either the collisional energy or the O2 rotational excitation giving rise to a continuous transition from a direct abstraction mechanism to an indirect insertion mechanism. The product state properties associated with a given collision energy of 135 meV and low rotational excitation of O2 are found to be consistent with the inverted SiO vibrational state distribution observed in a recent experiment. The SQM and PST statistical approaches, especially designed to deal with complex-forming reactions, provide an accurate description of the QCT total integral cross sections and opacity functions for all cases studied. The ability of such statistical treatments in providing reliable product state properties for a reaction dominated by a competition between abstraction and insertion pathways is carefully examined, and it is shown that a valuable information can be extracted over a wide range of selected initial conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The renewable nanofilms were found to have contact angles always below 90°, tunable Young modulus and hardness in the MPa range, as well as water vapour transmission rates which are increased by decreasing the silica ratio. • Using a quartz crystal microbalance in energy dissipation mode and atomic force microscopy it was found that BSA and lysozyme form rigid layers on the surface with surface coverage close to 30%, and that both protein layers decrease their thickness after their dehydration. • Cell culture experiments exhibited a good viability of the fibroblasts compared to ultra-low adhesion surfaces, which makes them potential candidates for biomedical applications. Abstract A comprehensive characterization of physical-chemical properties and biological interactions of ca. 200-nm-thick hybrid films based on silylated (inorganic part) castor oil (organic part) is proposed. A series of such nanofilms was fabricated and cross-linked by a sol-gel procedure, and their properties such as hydrophilicity, hardness and water vapour transmission rate were systematically studied as a function of the ratio of silylated agent to castor oil. It was found that the nanofilms have contact angles always below 90°, tunable Young modulus and hardness in the MPa range. Moreover, their water vapour transmission rates are increased by decreasing the silica ratio. The protein adsorption and cytocompatibility were evaluated using model proteins and cells. The adsorption of the proteins bovine serum albumin (BSA) and lysozyme was characterized using a quartz crystal microbalance in energy dissipation mode (QCM-D), and atomic force microscopy (AFM). The combination of the latter provided evidence for the different affinities of the proteins with the films. It was found that BSA and lysozyme form rigid layers on the surface with surface coverage close to 30%, and that both protein layers decrease their thickness after their dehydration. Finally, cell culture experiments exhibited a good viability of the fibroblasts compared to ultra-low adhesion surfaces, which makes them potential candidates for biomedical applications. [ABSTRACT FROM AUTHOR]

Monolithicpectin aerogels, aeropectins, were prepared via dissolution–gelation–coagulationand subsequent drying with supercritical CO2. Aeropectinhad pore sizes that varied from mesopores to small macropores andcompression moduli in the range from 4 to 18 MPa. Aeropectins showplastic deformation up to 60% strain before the pore walls collapse.Pectin aerogels have a thermal conductivity below that of air in ambientconditions, making them new thermal superinsulating fully biomass-basedmaterials. The contribution of gas and solid conduction plus radiativeheat transfer were determined and discussed. [ABSTRACT FROM AUTHOR]

The dynamics of the S ( 1 D) +HD reaction has been investigated in the low energy regime by means of a statistical quantum method and mean potential phase space theory. Statistical predictions for cross sections down to 10 − 4 eV and the corresponding isotope branching ratios have thus been calculated and compared with previous results from the literature. Integral cross sections are also extended up to 0.2 eV to compare with experimental excitation functions reported in the past. Differences between theoretical and experimental branching ratios regarding the two possible product channels, SD+H and SH+D, are observed. • Study of the S ( 1 D) +HD reaction with statistical techniques in the low energy regime. • Cross sections are compared with exact quantum mechanical and experimental values at a more extended temperature range. • Branching ratio between the two possible product channels, SH+D and SD+H, are still subject of discussion. [ABSTRACT FROM AUTHOR]

A correction to the article "A comparative study of the Si+O2→SiO+O reaction dynamics from quasiclassical trajectory and statistical based methods," that was published online on January 23, 2009 is presented.

The dynamics of the O+OH reaction on the ground state potential energy surface (PES) is investigated by means of the quasiclassical trajectory method and two statistical methods: phase space theory and statistical quantum method. Preliminary calculations with an exact quantum method are also reported. The quasiclassical trajectory calculations show evidence for a phase space bottleneck inhibiting the intramolecular energy transfer between the O–H and O–O bonds. As a result, the probability of the intermediate complex dissociating back toward the reactants is high, thereby yielding a reaction probability significantly lower than expected for a barrierless and exothermic reaction. The features of the PES, which are the cause of this dynamical effect, are identified. This is essentially the conservation of the equilibrium distance of the O–H bond, hardly changed by a close encounter with an oxygen atom. The statistical calculations, which do not take into account the PES in the complex region, yield a high reaction probability, much larger than the probability calculated from the dynamical methods, both classical and quantum. If the statistical cross sections are corrected by a scaling factor, which corresponds actually to scaling the capture probability, then a good agreement is observed between dynamical and statistical calculations of the product state distributions. The differential cross sections calculated with all the methods show a backward-forward symmetry, with sharp polarization peaks. The complex lifetime is divided into two parts by the bottleneck. During the first part, the system remains trapped in a small region of the phase space and has a high probability to dissociate back toward the reactants. This is a nonstatistical effect due to the PES shape. During the second part, fast intramolecular vibrational energy redistribution takes place, leading to a statistical distribution of energy on the rovibrational states of the products. These findings indicate that the O+OH reaction has mixed dynamics, both with statistical and nonstatistical aspects. [ABSTRACT FROM AUTHOR]

The possible existence of a complex-forming pathway for the H+O2 reaction has been investigated by means of both quantum mechanical and statistical techniques. Reaction probabilities, integral cross sections, and differential cross sections have been obtained with a statistical quantum method and the mean potential phase space theory. The statistical predictions are compared to exact results calculated by means of time dependent wave packet methods and a previously reported time independent exact quantum mechanical approach using the double many-body expansion (DMBE IV) potential energy surface (PES) [Pastrana et al., J. Phys. Chem. 94, 8073 (1990)] and the recently developed surface (denoted XXZLG) by Xu et al. [J. Chem. Phys. 122, 244305 (2005)]. The statistical approaches are found to reproduce only some of the exact total reaction probabilities for low total angular momenta obtained with the DMBE IV PES and some of the cross sections calculated at energy values close to the reaction threshold for the XXZLG surface. Serious discrepancies with the exact integral cross sections at higher energy put into question the possible statistical nature of the title reaction. However, at a collision energy of 1.6 eV, statistical rotationally resolved cross sections managed to reproduce the experimental cross sections for the H+O2(v=0,j=1)→OH(v′=1,j′)+O process reasonably well. [ABSTRACT FROM AUTHOR]

Dentin, enamel and the transition zone, called the dentin-enamel junction (DEJ), have an organization and properties that play a critical role in tooth resilience and in stopping the propagation of cracks. Understanding their chemical and micro-biomechanical properties is then of foremost importance. The aim of this study is to apply Brillouin microscopy on a complex biological structure, that is, the DEJ, and to compare these results with those obtained with Raman microscopy. Both techniques allow noncontact measurements at the microscopic scale. Brillouin microscopy is based on the interaction between acoustic phonons and laser photons and gives a relation between the frequency shift of the scattered light and the stiffness of the sample. Raman spectra contain peaks related to specific chemical bonds. Comparison of the Brillouin and Raman cartographies reveals correlations between mechanical and chemical properties. Indeed, the shapes of the phosphate content and stiffness curves are similar. The two spectroscopies give compatible values for the mean distance between two tubules, i.e., 4–6 µm. Moreover, for the first time, the daily cross striations of enamel could be studied, indicating a relationship between the variation in the phosphate concentration and the variation in the rigidity within the enamel prisms. We demonstrate here the possibility of using Brillouin scattering microscopy to both study complex biological materials such as the enamel-dentin junction and visualize secondary structures. Correlations between the chemical composition and mechanical properties could help in better understanding the tissue histology. • Enamel, dentine and junction are organized for lifetime resilience. • Mechanical mapping could be done on dentine and enamel with Brillouin microscopy. • Brillouin microscopy highlights the mechanical properties of tooth microstructure. • The peritubular and intertubular Brillouin shifts are different. • Daily cross striation in enamel could be scanned with Brillouin microscopy. [ABSTRACT FROM AUTHOR]

• An experimental study concerns ITZ and the cement paste/aggregate bond. • The cement paste and the bond are exposed to leaching. • The impact of ITZ on the mechanical properties of the bond is evaluated. • A microscopic study of ITZ accompanies observations on leaching. • Effects of leaching kinetics, chemical dissolution and cracking are discussed. An experimental program is oriented to the mechanical behaviour of the Interfacial Transition Zone (ITZ) exposed to leaching, for a single mix. Leaching kinetics of the degraded depth, measured through grey level on cross sections, reveals a maximum gap of 10 % between ITZ and bulk cement paste. ITZ, with a main thickness of 15 µm suffers a significant decalcification, which is reflected on the mechanical properties of the bond. Grey level, Calcium/Silicon (Ca/Si) molar ratio and Young's modulus in the degraded zone present similar evolution. Effect of ITZ causing cracking and then debonding is noticed, through chemical analysis, image observation and mechanical tests. [ABSTRACT FROM AUTHOR]

The excitation function of the S(1D) + D2 reaction was determined in a crossed molecular beam apparatus for collision energies ranging from 1817 to 47 J mol-1 in the near-cold regime. A very good overall agreement was found between experimental data and the theoretical results obtained using the ab initio potential energy surface built by Ho and coworkers and different methods: time-independent quantum dynamics (QM), semiclassical mean potential capture theory (sc-MPCT), and quasi-classical trajectories (QCT). The general trend of the experimental excitation function is well reproduced in most of the range by a simple capture calculation with an R-6 dispersion potential. The present results are discussed in the light of previous studies on the isotopic variants S(1D) + H2 and HD. [ABSTRACT FROM AUTHOR]

Recent calculations on the hydrogen-exchange reaction [Bouakline et al., J. Chem. Phys. 128, 124322 (2008)], have found strong geometric phase (GP) effects in the state-to-state differential cross-sections (DCS), at energies above the energetic minimum of the conical intersection (CI) seam, which cancel out in the integral cross-sections (ICS). In this article, we explain the origin of this cancellation and make other predictions about the nature of the reaction mechanisms at these high energies by carrying out quasiclassical trajectory (QCT) calculations. Detailed comparisons are made with the quantum results by splitting the quantum and the QCT cross-sections into contributions from reaction paths that wind in different senses around the CI and that scatter the products in the nearside and farside directions. Reaction paths that traverse one transition state (1-TS) scatter their products in just the nearside direction, whereas paths that traverse two transition states (2-TS) scatter in both the nearside and farside directions. However, the nearside 2-TS products scatter into a different region of angular phase-space than the 1-TS products, which explains why the GP effects cancel out in the ICS. Analysis of the QCT results also suggests that two separate reaction mechanisms may be responsible for the 2-TS scattering at high energies. [ABSTRACT FROM AUTHOR]