Post-dissociation Dynamics of N₂ on Ru(0001): How Far Can the “Hot” N Atoms Travel?

Due to the high barrier and large exoergicity, the dissociation of N2 impinging on Ru(0001) produces ballistic N atoms that can travel significant distances from the impact site, as shown by a recent scanning tunneling microscopy study [Wagner, J. J. Phys. Chem. C 2022, 126, 18333−18342]. In this work, the “hot” nitrogen atom dynamics following N2 dissociation is investigated theoretically on a high-dimensional potential energy surface based on a neural network representation of density functional theory data. Quasi-classical trajectory simulations for N2 dissociation with several initial conditions revealed that typically only one N atom undergoes significant migration, while the other is often trapped near the impact site. Regardless of the initial condition, the average final separation between the two N atoms is typically less than 10 Å, about 1 order of magnitude less than the experimental report (66 ± 28 Å). The relatively short migration distance of the hot N atom found in our simulations is attributed to a high diffusion barrier and fast energy dissipation to surface phonons. The theory–experiment discrepancy presents a challenge to the quantitative understanding of hot atom dynamics on metal surfaces

Control of Mode/Bond Selectivity and Product Energy Disposal by the Transition State: X + H₂O (X = H, F, O(³P), and Cl) Reactions

The ability to predict mode/bond selectivity and energy disposal is of central importance for controlling chemical reactions. We argue that the transition state plays a critical role in state-to-state reactivity and propose a simple sudden model based on coupling with the reaction coordinate at the transition state. The applicability of this so-called sudden vector projection (SVP) model is examined for several prototypical atom–triatom, namely, X + H₂O (X = H, F, O­(³P), and Cl) reactions. It is shown that the SVP model is capable of qualitatively predicting experimental and full-dimensional quantum dynamical results, including those reported in this work, for these polyatomic reactions. These results, and those for other reactions, suggest that the SVP model offers a general paradigm for understanding quantum state resolved reactivity in bimolecular reactions

Quantum Mechanical/Molecular Mechanical and Density Functional Theory Studies of a Prototypical Zinc Peptidase (Carboxypeptidase A) Suggest a General Acid−General Base Mechanism

Carboxypeptidase A is a zinc-containing enzyme that cleaves the C-terminal residue in a polypeptide substrate. Despite much experimental work, there is still a significant controversy concerning its catalytic mechanism. In this study, the carboxypeptidase A-catalyzed hydrolysis of the hippuryl-l-Phe molecule (kcat = 17.7 ± 0.7 s−1) is investigated using both density functional theory and a hybrid quantum mechanical/molecular mechanical approach. The enzymatic reaction was found to proceed via a promoted-water pathway with Glu270 serving as the general base and general acid. Free-energy calculations indicate that the first nucleophilic addition step is rate-limiting, with a barrier of 17.9 kcal/mol. Besides activating the zinc-bound water nucleophile, the zinc cofactor also serves as an electrophilic catalyst that stabilizes the substrate carbonyl oxygen during the formation of the tetrahedral intermediate. In the Michaelis complex, Arg127, rather than Zn(II), is responsible for the polarization of the substrate carbonyl and it also serves as the oxyanion hole. As a result, its mutation leads to a higher free-energy barrier, in agreement with experimental observations

Modulations of Transition-State Control of State-to-State Dynamics in the F + H₂O → HF + OH Reaction

The full-dimensional quantum dynamics of the F + H₂O → HF + OH reaction is investigated at the state-to-state level for the first time using a transition-state wave packet method on an accurate global potential energy surface. It is found that the H₂O rotation enhances the reactivity and the product-state distribution is dominated by HF vibrational excitation while the OH moiety serves effectively as a spectator. These observations underscore the transition-state control of the reaction dynamics, as both the H₂O rotational and HF vibrational modes are strongly coupled to the reaction coordinate at the transition state. It is also shown that the transition-state dominance of the reaction dynamics is modulated by other features on the potential energy surface, such as the prereaction well

Full-Dimensional Quantum Calculations of Vibrational Levels of NH₄⁺ and Isotopomers on An Accurate Ab Initio Potential Energy Surface

Vibrational energy levels of the ammonium cation (NH₄⁺) and its deuterated isotopomers are calculated using a numerically exact kinetic energy operator on a recently developed nine-dimensional permutation invariant semiglobal potential energy surface fitted to a large number of high-level ab initio points. Like CH₄, the vibrational levels of NH₄⁺ and ND₄⁺ exhibit a polyad structure, characterized by a collective quantum number <i>P</i> = 2­(<i>v</i>₁ + <i>v</i>₃) + <i>v</i>₂ + <i>v</i>₄. The low-lying vibrational levels of all isotopomers are assigned and the agreement with available experimental data is better than 1 cm^–1

Dynamics of “Hot” Oxygen Atoms on Ag(100) Surface upon O₂ Dissociation

The dynamics of ballistic adsorbates on metal surfaces are not only important for understanding energy dissipation but also of practical relevance in an array of important applications including corrosion and heterogeneous catalysis. In this work, we examine the early dynamics of “hot” O atoms produced by dissociative chemisorption of O2 on a Ag(100) surface, taking advantage of a high-fidelity machine learned high-dimensional potential energy surface based on first-principles data. Our classical trajectory simulations revealed that the experimentally observed large O–O separations (2–4 nm) can only be reached with hyperthermal incident O2. With thermally impinging O2, the calculated separation between the equilibrated O atoms is about 1 order of magnitude shorter (∼0.3 nm). The relatively low mobility of the “hot” O atoms on this surface is attributed to the fast energy dissipation to surface phonons and a relatively high diffusion barrier. In addition, the O atom diffusion exhibits strong anisotropy dictated by the potential energy surface

Dynamics of “Hot” Oxygen Atoms on Ag(100) Surface upon O₂ Dissociation

The dynamics of ballistic adsorbates on metal surfaces are not only important for understanding energy dissipation but also of practical relevance in an array of important applications including corrosion and heterogeneous catalysis. In this work, we examine the early dynamics of “hot” O atoms produced by dissociative chemisorption of O2 on a Ag(100) surface, taking advantage of a high-fidelity machine learned high-dimensional potential energy surface based on first-principles data. Our classical trajectory simulations revealed that the experimentally observed large O–O separations (2–4 nm) can only be reached with hyperthermal incident O2. With thermally impinging O2, the calculated separation between the equilibrated O atoms is about 1 order of magnitude shorter (∼0.3 nm). The relatively low mobility of the “hot” O atoms on this surface is attributed to the fast energy dissipation to surface phonons and a relatively high diffusion barrier. In addition, the O atom diffusion exhibits strong anisotropy dictated by the potential energy surface

Dynamics of “Hot” Oxygen Atoms on Ag(100) Surface upon O₂ Dissociation

The dynamics of ballistic adsorbates on metal surfaces are not only important for understanding energy dissipation but also of practical relevance in an array of important applications including corrosion and heterogeneous catalysis. In this work, we examine the early dynamics of “hot” O atoms produced by dissociative chemisorption of O2 on a Ag(100) surface, taking advantage of a high-fidelity machine learned high-dimensional potential energy surface based on first-principles data. Our classical trajectory simulations revealed that the experimentally observed large O–O separations (2–4 nm) can only be reached with hyperthermal incident O2. With thermally impinging O2, the calculated separation between the equilibrated O atoms is about 1 order of magnitude shorter (∼0.3 nm). The relatively low mobility of the “hot” O atoms on this surface is attributed to the fast energy dissipation to surface phonons and a relatively high diffusion barrier. In addition, the O atom diffusion exhibits strong anisotropy dictated by the potential energy surface

Dynamics of “Hot” Oxygen Atoms on Ag(100) Surface upon O₂ Dissociation

The dynamics of ballistic adsorbates on metal surfaces are not only important for understanding energy dissipation but also of practical relevance in an array of important applications including corrosion and heterogeneous catalysis. In this work, we examine the early dynamics of “hot” O atoms produced by dissociative chemisorption of O2 on a Ag(100) surface, taking advantage of a high-fidelity machine learned high-dimensional potential energy surface based on first-principles data. Our classical trajectory simulations revealed that the experimentally observed large O–O separations (2–4 nm) can only be reached with hyperthermal incident O2. With thermally impinging O2, the calculated separation between the equilibrated O atoms is about 1 order of magnitude shorter (∼0.3 nm). The relatively low mobility of the “hot” O atoms on this surface is attributed to the fast energy dissipation to surface phonons and a relatively high diffusion barrier. In addition, the O atom diffusion exhibits strong anisotropy dictated by the potential energy surface

Dynamics of “Hot” Oxygen Atoms on Ag(100) Surface upon O₂ Dissociation

The dynamics of ballistic adsorbates on metal surfaces are not only important for understanding energy dissipation but also of practical relevance in an array of important applications including corrosion and heterogeneous catalysis. In this work, we examine the early dynamics of “hot” O atoms produced by dissociative chemisorption of O2 on a Ag(100) surface, taking advantage of a high-fidelity machine learned high-dimensional potential energy surface based on first-principles data. Our classical trajectory simulations revealed that the experimentally observed large O–O separations (2–4 nm) can only be reached with hyperthermal incident O2. With thermally impinging O2, the calculated separation between the equilibrated O atoms is about 1 order of magnitude shorter (∼0.3 nm). The relatively low mobility of the “hot” O atoms on this surface is attributed to the fast energy dissipation to surface phonons and a relatively high diffusion barrier. In addition, the O atom diffusion exhibits strong anisotropy dictated by the potential energy surface