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We explore the application of reduced density matrix-based approaches to molecules interacting with the lattice vibrations of metals, an interaction responsible for the temperature dependence of many of the fundamental steps of catalysis. We avoid the use of simple models for the bath and instead use density functional theory to compute all molecule–phonon interactions and the properties of the lattice phonons, for methane scattering from Ir(111). We find that while the large metal mass leads to long bath correlation times, these are not significantly longer than the time over which the reduced density matrix changes due to interactions with the bath. We show that the neglect of memory is reasonable and the use of the Redfield equation is justified. We also show how the commonly used rotating wave approximation is far too severe for this scattering problem. A less restrictive approximation that is nearly exact for our system gives an equation of motion in the Lindblad form. As a result, the Monte Carlo wave packet methods can be used to describe gas–phonon scattering, guaranteeing positivity, and with all couplings derived from first-principles.

We implement a fully quantum mechanical study of methane trapping on Ir(111), where the phonons, the molecule–surface interaction, and the molecule–phonon coupling are all computed from first-principles. We find that both the surface corrugation and the phonon coupling vary strongly with molecular orientation and that there is a “chemical” aspect to this due to the catalytic nature of the metal. For example, molecules with reactive orientations can approach close to surface sites with low barriers to dissociation. Moreover, lattice motion can lower the barrier to dissociation, leading to unusual behavior for the phonon coupling. We find good agreement with experiment and two recent classical studies if we average our potential energy surface over several orientations of the molecule. We also find reasonable agreement with a recent study of methane diffraction, although we show that diffraction does not play a major role in trapping on the smooth Ir(111) surface and that trapping obeys normal energy scaling, consistent with experiment. We show that the trapping probability can be sensitive to the temperature at both high and low incidence energies. Relaxation and desorption of trapped particles are examined.

The indirect chemisorption of methane on a transition metal, where the incident molecule first traps onto the surface and then reacts from a physisorbed molecular state, has only been observed on Ir(111) and Ir(110) at very low collision energies. We use quantum scattering methods to describe the direct reaction of methane on Ir(111) at high energy and rate theory to examine the indirect pathway at low energy. Overall, we find good agreement with the experiment with respect to the variation of sticking with the incident energy, surface temperature, and vibrational state. Compared with methane dissociation on other metals, vibrational excitation is found to be less effective at promoting the reaction, while coupling to the lattice motion is unusually strong. We show how step defects, even at low concentrations, can contribute significantly to indirect chemisorption. We explore indirect chemisorption on Ni(111) and Pt(111) and find that the indirect path can be important when relaxed lattice barriers are sufficiently low and the temperature is sufficiently high so that the indirect sticking is within detection limits and the incident energy is low enough so that the trapping is large and the direct component is small.

Selecting 3D regions-of-interest (ROI) in surface geometry is essential for 3D modeling, but few 3D user interfaces using fully manual input for ROI selection exist. Furthermore, their relative performance is not well studied. We present an evaluation comparing three ROI techniques: Volume Cube [Ulinski et al. 2007], Slice-n- Swipe [Bacim et al. 2014], and Yea Big Yea High Selection [Jackson et al. 2018]. Results show that Yea Big Yea High is best for tasks requiring high accuracy and speed, but modifications may be needed for use in dense geometry or with non-convex ROI.

This chapter presents an approach to designing expressive three-dimensional (3D) user interfaces that make use of handheld input devices tracked in 3D space to go beyond a simple pointing metaphor. It considers a series of three examples that build upon each other to demonstrate how sophisticated 6-degree-of-freedom, beyond-pointing, bimanual virtual reality (VR) user interfaces can be built upon this framework. Although event-based user interfaces are common in desktop computing, there are several important nuances in VR. The state machine design pattern that developers suggest for programming VR interfaces helps programmers to track and respond appropriately to changes in context. The user interface to select curves must be flexible and controlled enough that users are able to indicate their desired selection regardless of the particular texture. The chapter describes how to implement contextual constraints to improve control of 3D User Interfaces.

We explore the dynamics and kinetics of methane dissociation on the steps of Ni(211) and the terraces of Ni(111), as models for step and terrace sites, respectively, on a real Ni catalyst. A quantum approach is used to compute state resolved sticking probabilities, S0, and the thermally averaged sticking is computed from both S0 and more standard transition state methods. While the barriers can be much lower on the step edges, the terrace atoms can make important contributions to the overall reactivity if the step density is not too high and/or at higher temperatures. At 500 K, we find that for reaction on the step edge, sticking is dominated by molecules with either one or two quanta of bending vibration excited, with translational energies of about 0.10-0.35 eV or 0-0.2 eV, respectively. These energies are well below the rigid lattice activation energies, and reaction requires both a significant conversion of vibrational energy into motion along the reaction path and puckering of the lattice atom over which the molecule dissociates. We show that the average amount of puckering, which lowers the barrier to reaction, is about 0.28 A at 500 K. Reactions are dominated by collisions at impact sites within a few tenths of an A of the minimum barrier pathway at the step edge. Our computed sticking probabilities for reaction on the step at 500 K are in good agreement with available experimental data.

The heat of adsorption and sticking probability of methyl iodide were measured on Ni(111) at 100 and 160 K using single-crystal adsorption calorimetry (SCAC). At 100 K, methyl iodide adsorbs molecularly with a heat of 102 kJ/mol on terrace sites in the low-coverage limit, giving a standard enthalpy of formation (ΔHf°) of CH3I(ad) of −87 kJ/mol. A heat of 122 kJ/mol is also measured on defect sites, probably step edges. Calorimetry of the dissociative adsorption of methyl iodide on Ni(111) at 160 K yielded an integral heat of adsorption of −270 kJ/mol at 0.04 ML, providing the energetics of adsorbed methyl, with ΔHf°[CH3(ad)] = −71 kJ/mol and a CH3–Ni(111) bond enthalpy of 218 kJ/mol. This is 22 kJ/mol stronger than the reported value for H3C–Pt(111) bonds, explaining the greater activity of Ni catalysts for hydrogenolysis in comparison to Pt. The measured energetics for methyl were compared to density functional theory (DFT) calculations from previous literature, showing that these methods systematically ...

The dissociative chemisorption of small molecules such as methane and water on metal surfaces is a key step in many important catalyzed reactions. However, it has only very recently become possible to directly compare theory with molecular beam studies of these reactions. For most experimental conditions, such a comparison requires accurate methods for introducing the effects of lattice motion into quantum reactive scattering calculations. We examine these methods and their recent application to methane and water dissociative chemisorption. New results are presented for CO2 chemisorption and methane dissociation at step edges. The type of molecule–lattice coupling that leads to a strong variation in the dissociative sticking of methane with temperature is shown to occur for many polyatomic–metal systems. Improvements to these models are discussed. The ability to accurately compare theory with molecular beam experiments should lead to improved density functionals and consequently more accurate thermal rate...

The dissociative chemisorption of CH

Methane dissociation on the step and terrace sites of a Pt(211) single crystal was studied by reflection absorption infrared spectroscopy (RAIRS) at a surface temperature of 120 K. The C-H stretch RAIRS signal of the chemisorbed methyl product species was used to distinguish between adsorption on step and terrace sites allowing methyl uptake to be monitored as a function of incident kinetic energy for both sites. Our results indicate a direct dissociation mechanism on both sites with higher reactivity on steps than on terraces consistent with a difference in an activation barrier height of at least 30 kJ/mol. State-specific preparation of incident CH4 with one quantum of antisymmetric (ν3) stretch vibration further increases the CH4 reactivity enabling comparison between translational and vibrational activation on both steps and terraces. The reaction is modeled with first principles quantum theory that accurately describes dissociative chemisorption at different sites on the surface.

A quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore CHD3 dissociation on Ni(111). Symmetric stretch vibrations are shown to have larger efficacies for promoting reaction and bond selectivity than antisymmetric stretches. Mode softening, associated with a localization of vibrational energy on the reacting bond, correlates adiabatically with the symmetric stretch. This lowers the barrier on that vibrationally adiabatic reaction path. At energies below these barriers, reaction occurs via nonadiabatic transitions to lower-energy vibrational states at the avoided crossings. This sudden behavior preserves energy localization on the reactive bond and converts vibrational energy into bond breaking. One of the antisymmetric stretches can typically not couple to the other states due to symmetry, eliminating these pathways. The ν1 stretch has a large efficacy and can give 100% C–H cleavage selectivity. Both CD3 stretches have reasonable efficacies, and both promote C–D ...

Accurately simulating heterogeneously catalyzed reactions requires reliable barriers for molecules reacting at defects on metal surfaces, such as steps. However, first-principles methods capable of computing these barriers to chemical accuracy have yet to be demonstrated. We show that state-resolved molecular beam experiments combined with ab initio molecular dynamics using specific reaction parameter density functional theory (SRP-DFT) can determine the molecule-metal surface interaction with the required reliability. Crucially, SRP-DFT exhibits transferability: the functional devised for methane reacting on a flat (111) face of Pt (and Ni) also describes its reaction on stepped Pt(211) with chemical accuracy. Our approach can help bridge the materials gap between fundamental surface science studies on regular surfaces and heterogeneous catalysis in which defected surfaces are important.

The dissociative chemisorption of methane on metal surfaces is of fundamental and practical interest, being a rate-limiting step in the steam reforming process. The reaction is best modeled with quantum dynamics calculations, but these are currently not guaranteed to produce accurate results because they rely on potential energy surfaces based on untested density functionals and on untested dynamical approximations. To help overcome these limitations, here we present for the first time statistically accurate reaction probabilities obtained with ab initio molecular dynamics (AIMD) for a polyatomic gas-phase molecule reacting with a metal surface. Using a general purpose density functional, the AIMD reaction probabilities are in semiquantitative agreement with new quantum-state-resolved experiments on CHD3 + Pt(111). The comparison suggests the use of the sudden approximation for treating the rotations even though CHD3 has large rotational constants and yields an estimated reaction barrier of 0.9 eV for CH4 + Pt(111).

The dissociative chemisorption of methane on Pt(110)-(1×2) is examined, with a focus on how the reaction dynamics are modified by the motion of the lattice atoms. The barriers to dissociation are found to be lowest at the step edges. The relaxation of the lattice in the presence of the dissociating molecule is found to be far more complicated than on the smooth surfaces of Pt and Ni. The dissociative sticking probabilities are computed using a full-dimensional treatment based on the reaction path Hamiltonian that includes all 15 molecular degrees of freedom and the effects of lattice motion. The potential energy surface and all parameters in our model are computed from first principles. The effects of lattice motion are strong, but not significantly larger than for dissociation on smoother surfaces. Vibrational excitation of the molecule can significantly enhance reactivity, though this effect varies from mode to mode. Agreement with recent experiments with regard to the variation of reactivity with translational energy and substrate temperature is good.

A quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore the dissociative chemisorption of CO

Quantum state resolved reactivity measurements probe the role of vibrational symmetry on the vibrational activation of the dissociative chemisorption of CH

Accurately simulating heterogeneously catalyzed reactions requires reliable barriers for molecules reacting at defects on metal surfaces, such as steps. However, first- principles methods capable of computing these barriers to chemical accuracy have yet to be demonstrated. We show that state-resolved molecular beam experiments combined with ab initio molecular dynamics using specific reaction parameter density functional theory (SRP-DFT) can determine the molecule-metal surface interaction with the required reliability. Crucially, SRP-DFT exhibits transferability: the functional devised for methane reacting on a flat (111) face of Pt (and Ni) also describes its reaction on stepped Pt(211) with chemical accuracy. Our approach can help bridge the materials gap between fundamental surface science studies on regular surfaces and heterogeneous catalysis in which defected surfaces are important.

The dissociative chemisorption of CH4 on Pt(111) was studied using quantum state-resolved methods at a surface temperature (T(s)) of 150 K where the nascent reaction products CH3(ads) and H(ads) are stable and accumulate on the surface. Most previous experimental studies of methane chemisorption on transition metal surfaces report only the initial sticking coefficients S0 on a clean surface. Reflection absorption infrared spectroscopy (RAIRS), used here for state resolved reactivity measurements, enables us to monitor the CH3(ads) uptake during molecular beam deposition as a function of incident translational energy (E(t)) and vibrational state (ν3 anti-symmetric C-H stretch of CH4) to obtain the initial sticking probability S0, the coverage dependence of the sticking probability S(θ) and the CH3(ads) saturation coverage θ(sat). We observe that both S0 and θ(sat) increase with increasing E(t) as well as upon ν3 excitation of the incident CH4 which indicates a coverage dependent dissociation barrier height for the dissociation of CH4 on Pt(111) at low surface temperature. This interpretation is supported by density functional calculations of barrier heights for dissociation, using large supercells containing one or more H and/or methyl adsorbates. We find a significant increase in the activation energies with coverage. These energies are used to construct simple models that reasonably reproduce the uptake data and the observed saturation coverages.

The objective of this project has been to develop realistic theoretical models for gas-surface interactions, with a focus on processes important in heterogeneous catalysis. The dissociative chemisorption of a molecule on a metal is a key step in many catalyzed reactions, and is often the rate-limiting step. We have explored the dissociative chemisorption of H2, H2O and CH4 on a variety of metal surfaces. Most recently, our extensive studies of methane dissociation on Ni and Pt surfaces have fully elucidated its dependence on translational energy, vibrational state and surface temperature, providing the first accurate comparisons with experimental data. We have explored Eley-Rideal and hot atom reactions of H atoms with H- and C-covered metal surfaces. H atom interactions with graphite have also been explored, including both sticking and Eley-Rideal recombination processes. Again, our methods made it possible to explain several experiments studying these reactions. The sticking of atoms on metal surfaces has also been studied. To help elucidate the experiments that study these processes, we examine how the reaction dynamics depend upon the nature of the molecule-metal interaction, as well as experimental variables such as substrate temperature, beam energy, angle of impact, and the internal states of the molecules. Electronicmore » structure methods based on Density Functional Theory are used to compute each molecule-metal potential energy surface. Both time-dependent quantum scattering techniques and quasi-classical methods are used to examine the reaction or scattering dynamics. Much of our effort has been directed towards developing improved quantum methods that can accurately describe reactions, as well as include the effects of substrate temperature (lattice vibration).« less

A quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore CH4 dissociation on Pt(111). Computed sticking probabilities for molecules in the ground, 1v3 and 2v3, states are in very good agreement with the available experimental data, reproducing the variation in reactivity with collision energy and vibrational state. As was found in similar studies on Ni(100) and Ni(111), exciting the 1v1 symmetric stretch of CH4 is more effective at promoting the dissociative chemisorption of CH4 than exciting the 1v3 antisymmetric stretch. This behavior is explained in terms of symmetry, mode-softening, and nonadiabatic transitions between vibrationally adiabatic states. We find that the efficacies of the bending modes for promoting reaction are reasonably large, and similar to the 1v3 state. The vibrational efficacies for promoting reaction on Ni(111) are larger than for reaction on Pt(111), due to the larger nonadiabatic couplings. Our computed sticking probabilities are in good agreement with results from recent ab initio molecular dynamics and reactive force field studies.

The dissociative chemisorption of CH4 on the stepped Ni(211) surface is explored. The H and CH3 fragments preferentially bind to the surface along the step edge, and the barriers to dissociation are lowest over the step edge atoms, with activation energies of 0.57 and 0.69 eV, depending upon the orientation of the dissociating bond. The activation energy for dissociation over a terrace atom is much larger, 0.99 eV. Quantum scattering calculations show that dissociation over the lowest barrier step edge site dominates the reactive scattering, except at very high collision energies, where the second step edge transition state becomes important. Even at incident energies of 1.0 eV, reaction over the terrace atoms contributes only about 3% to the total dissociative sticking. The symmetric stretch excitation has the largest efficacy for promoting reaction, with the other modes having somewhat smaller efficacies. While the vibrational properties of the step edge atoms are different from those on the terrace, reactions at both sites exhibit a similar variation with temperature. We find good agreement with experimental measurements of the thermally averaged sticking probability on a Ni step edge.

Three-dimensional modeling has long been regarded as an ideal application for virtual reality (VR), but current VR-based 3D modeling tools suffer from two problems that limit creativity and applicability: (1) the lack of control for freehand modeling, and (2) the difficulty of starting from scratch. To address these challenges, we present Lift-Off , an immersive 3D interface for creating complex models with a controlled, handcrafted style. Artists start outside of VR with 2D sketches, which are then imported and positioned in VR. Then, using a VR interface built on top of image processing algorithms, 2D curves within the sketches are selected interactively and “lifted” into space to create a 3D scaffolding for the model. Finally, artists sweep surfaces along these curves to create 3D models. Evaluations are presented for both long-term users and for novices who each created a 3D sailboat model from the same starting sketch. Qualitative results are positive, with the visual style of the resulting models of animals and other organic subjects as well as architectural models matching what is possible with traditional fine art media. In addition, quantitative data from logging features built into the software are used to characterize typical tool use and suggest areas for further refinement of the interface.

Studies exploring how vibrational energy (Evib) promotes chemical reactivity most often focus on molecular reagents, leaving the role of substrate atom motion in heterogeneous interfacial chemistry underexplored. This combined theoretical and experimental study of methane dissociation on Ni(111) shows that lattice atom motion modulates the reaction barrier height during each surface atom's vibrational period, which leads to a strong variation in the reaction probability (S0) with surface temperature (Tsurf). State-resolved beam-surface scattering studies at Tsurf = 90 K show a sharp threshold in S0 at translational energy (Etrans) = 42 kJ/mol. When Etrans decreases from 42 kJ/mol to 34 kJ/mol, S0 decreases 1000-fold at Tsurf = 90 K, but only 2-fold at Tsurf = 475 K. Results highlight the mechanism for this effect, provide benchmarks for DFT calculations, and suggest the potential importance of surface atom induced barrier height modulation in heterogeneously catalyzed reactions, particularly on structurally labile nanoscale particles and defect sites.

A fully quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore the dissociative chemisorption of H2O, HOD, and D2O on Ni(111). For this late barrier system, excitation of both the bending and stretching modes significantly enhances dissociative sticking. The vibrational efficacies vary somewhat from mode-to-mode but are all relatively close to one, in contrast to methane dissociation, where the behavior is less statistical. Similar to methane dissociation, the motion of lattice atoms near the dissociating molecule can significantly modify the height of the barrier to dissociation, leading to a strong variation in dissociative sticking with substrate temperature. Given a rescaling of the barrier height, our results are in reasonable agreement with measurements of the dissociative sticking of D2O on Ni(111), for both laser-excited molecules with one or two quanta of excitation in the antisymmetric stretch and in the absence of laser excitation. Even without laser excitation, the beam contains vibrationally excited molecules populated at the experimental source temperature, and these make significant contributions to the sticking probability. At high collision energies, above the adiabatic barrier heights, our results correlate with these barrier heights and mode softening effects. At lower energies, dissociative sticking occurs primarily via vibrationally nonadiabatic pathways. We find a preference for O–H over O–D bond cleavage for ground state HOD molecules at all but the highest collision energies, and excitation of the O–H stretch gives close to 100% O–H selectivity at lower energies. Excitation of the O–D stretch gives a lower O–D cleavage selectivity, as the interaction with the surface leads to energy transfer from the O–D stretch into the O–H bond, when mode softening makes these vibrations nearly degenerate.

Recent experiments suggest that the high hydrogen storage capacity in graphite nanostructures might be associated with adsorption on the edges. First-principles calculations are used to study the structure and energetics of H chemisorption on graphite zigzag edges. The properties of both singly and doubly hydrogenated edges are examined. Molecular hydrogen can dissociatively adsorb on the edge directly, with small activation barriers to the formation of either singly or doubly hydrogenated structures. A new model for the location of adsorbed H is proposed.

The Eley–Rideal reactions of H atoms with Cl adsorbed on Au(111) surfaces are examined. Electronic structure calculations based on density functional theory are used to construct a model potential energy surface. Both quantum and quasiclassical methods are used to compute reaction cross sections and product state distributions. Steering of the incident H atom towards the adsorbed Cl leads to relatively large reaction cross sections of 2–3 A2. The product HCl in this strongly exothermic reaction has over an eV of energy in vibrational motion, and a bit less than one eV each in rotation and translation.

An accurate system-bath model to investigate the quantum dynamics of hydrogen atoms chemisorbed on graphene is presented. The system comprises a hydrogen atom and the carbon atom from graphene that forms the covalent bond, and it is described by a previously developed 4D potential energy surface based on density functional theory ab initio data. The bath describes the rest of the carbon lattice and is obtained from an empirical force field through inversion of a classical equilibrium correlation function describing the hydrogen motion. By construction, model building easily accommodates improvements coming from the use of higher level electronic structure theory for the system. Further, it is well suited to a determination of the system-environment coupling by means of ab initio molecular dynamics. This paper details the system-bath modeling and shows its application to the quantum dynamics of vibrational relaxation of a chemisorbed hydrogen atom, which is here investigated at T = 0 K with the help of the multi-configuration time-dependent Hartree method. Paper II deals with the sticking dynamics.

Adsorption of H and D on HOPG surfaces was studied with thermal desorption (TDS), electronic (ELS), and high-resolution electron-energy-loss (HREELS) spectroscopies. After admission of H (D) from thermal (2000 K) atom sources to clean graphite surfaces TD spectra revealed recombinative molecular H2 (D2) desorption in a main peak around 445 K (490 K) and a minor peak at 560 K (580 K). After admission of higher fluences the main peak shifts to 460 K (500 K) and develops a shoulder at 500 K (540 K). The saturation coverages were calculated as 0.4±0.2 for H and D and initial sticking coefficients of 0.4±0.2 were obtained. Through leading edge analysis of the TD spectra desorption activation energies for H and D were determined as 0.6 and 0.95 eV, respectively. EL spectra suggest a 16% loss of the sp2 character of the surface carbon 2sp electrons upon D adsorption. HREEL spectra of H (D) graphite covered surfaces reveal in addition to two graphite-intrinsic optical phonon losses vibrational features at 1210 an...

The kinetics of HD formation during admission of H atoms to D covered HOPG surfaces was measured at 150 K as a function of the initial D coverage. The phenomenology of the HD kinetics is as expected for an Eley-Rideal reaction or hot-atom reaction scenario with preference for reaction over sticking for hot atoms. It can be described by an abstraction cross-section, which varies between 17 (low coverage) and 4 A 2 (high coverage). The large abstraction cross-section at low coverages is in accordance with a steering effect of the adsorbed D on the incoming H as predicted by theory.

A coupled wave vector formalism is applied to compute the reduced density matrix for dissociation and inelastic scattering of D2 molecules on Cu surfaces at finite temperature. The effect of lattic...

Quasiclassical methods are used to simulate the interactions of H or D atom beams with D- or H-covered Ni(100) surfaces. The Ni substrate is treated as a multilayer slab, and the Ni atoms are allowed to move. The model potential energy surface is fit to the results of detailed total-energy calculations based on density functional theory. Most of the incident atoms trap to form hot atoms, which can eventually react with an adsorbate, or dissipate their energy and stick. The incident atom is found to lose several tenths of an eV of energy into the metal, upon initially colliding with the surface. This limits reflection to a few percent, at all coverages, and secondary reactions between adsorbates are significantly lowered. Long time hot atom reactions are also found to be damped out by the inclusion of lattice motion, leading to increased sticking, even at high coverages where dissipation into the adsorbates should be the primary energy loss mechanism. Overall, the inclusion of lattice motion is found to improve agreement with experiment.

Ab initio methods based on density functional theory are used to compute the potential energy surface for the motion of H from the subsurface onto the Ni(1 1 1) surface. Transition state theory is used to calculate rate constants for this resurfacing. The influences of tunneling and lattice relaxation are computed and discussed, and comparisons are made with measured vibrational and thermal desorption spectra. Due to the metastable nature of the subsurface octahedral site, the resurfacing H has an excess energy of roughly 1 eV. The resulting hot and highly mobile atoms can engage in unique chemistry with surface-adsorbed species.

Results from electronic structure studies and quantum scattering calculations are presented for the reaction of gas-phase H atoms with H atoms adsorbed onto a graphite surface to form H2(g). H can chemisorb on graphite directly over a carbon atom, with the carbon puckering out of the surface plane by several tenths of an A. Using an ab initio approach based on the density functional theory, and treating the graphite substrate as a slab, we compute the potential energy surface for this reaction, for three cases. In the first case the adsorbed H is initially in the chemisorbed state and the lattice is held fixed in the puckered position during the reaction. In the second case the adsorbed H is initially in the chemisorbed state, but the lattice is allowed to fully relax for each configuration of the two H atoms. In the third case the H initially on the surface is in the physisorbed state. We use a fully quantum mechanical scattering approach to compute reaction cross sections and product H2 translational, r...