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The comprehensive picture of the fragmentation behaviour of H2S has been provided by detecting the H, S(1D) and S(1S) atom products at wavelengths 155–120 nm.

The photoinduced unimolecular decay of the electronically excited HCO(Ã2A′′) is investigated in a combined experimental–theoretical study.

We report the first full-dimensional quantum mechanical calculations of the ro-vibrational inelastic scattering dynamics between water molecules and argon atoms on an accurate potential energy surface, using a recently developed time-independent quantum method based on the close-coupling approach.

Thermal rate coefficients and kinetic isotope effects have been calculated for an important atmospheric reaction H/D + O3 → OH/OD + O2 based on an accurate permutation invariant polynomial-neural network potential energy surface, using ring polymer molecular dynamics (RPMD), quasi-classical trajectory (QCT) and variational transition-state theory (VTST) with multidimensional tunneling. The RPMD approach yielded results that are generally in better agreement with experimental rate coefficients than the VTST and QCT ones, especially at low temperatures, attributable to its capacity to capture quantum effects such as tunneling and zero-point energy. The theoretical results support one group of existing experiments over the other. In addition, rate coefficients for the D + O3 → OD + O2 reaction are also reported using the same methods, which will allow a stringent assessment of future experimental measurements, thus helping to reduce the uncertainty in the recommended rate coefficients of this reaction.

The key to reducing the cost of proton-exchange-membrane fuel cells (PEMFCs) is to develop highly efficient non-precious metal catalysts for the oxygen reduction reaction (ORR). Herein, we fabricated Co/Zn atomic dual-sites anchored on N doped carbon nanofibers (Co/Zn–NCNF) via electrospinning, carbonization and post-treatment technologies. Aberration-corrected STEM microscopy verifies the existence of uniformly dispersed Co/Zn atomic pairs within the NCNF. X-ray adsorption fine structure spectroscopy combined with the fitting and calculated results further ascertain the coordination structure of Co/Zn dual-sites with a configuration of N2CoN2ZnN2. Such a Co/Zn–NCNF catalyst exhibits greatly enhanced ORR activity with onset and half-wave potentials of 0.997 V and 0.797 V/RHE in an acidic electrolyte, compared to the Co or Zn mono-doped sample. Density functional theory calculations reveal that the novel N2CoN2ZnN2 structure, different from the traditional Co–N4 or Zn–N4, could largely lower the dissociative barrier of the *OOH intermediate during the ORR, thereby boosting the electrocatalytic activity. Finally, the H2–O2 PEMFC assembled using Co/Zn–NCNF as a cathodic catalyst displays a maximum power density of 0.603 W cm−2 together with a remarkable stability of ca. 0.65 V after 150 h discharging at a current density of 400 mA cm−2, paving the way for the future development of non-precious metal PEMFCs.

The reaction OH + HO2 → H2O + O2 is of great significance in interstellar media, the atmosphere, and combustion. In addition, it presents a prototypical reaction between two non-atom radical species. However, the temperature dependence of its rate coefficients has been debated for several decades. In this work, the rate coefficients are revisited by the quasi-classical trajectory (QCT) approach. To this end, a globally accurate full-dimensional potential energy surface of the ground triplet state for the title reaction is constructed using the permutation invariant polynomial-neural network (PIP-NN) method based on 108 000 points calculated at the level of CCSD(T)-F12a/AVTZ, in which particular attention is paid to the initial guess in the preceding Hartree–Fock procedure to obtain reliable ab initio energies. The QCT rate coefficients are compared to available experimental and theoretical results. It has been found that not only the trend, but also the magnitude, i.e. the large negative temperature dependence at low temperatures, and slightly positive temperature dependence at high temperatures, are consistent with some experiments.

Intersystem crossing is a common and important nonadiabatic process in molecular systems, and its first-principles characterization requires accurate descriptions of both the electronic structure and nuclear dynamics. Here, we report an accurate full-dimensional quantum dynamical investigation of collisional quenching of the excited state C(1D) atom to its ground state C(3P) counterpart by N2, which is an important process in both combustion and interstellar media, using full-dimensional ab initio potential energy surfaces and spin–orbit couplings. Satisfactory agreement with experimental rate coefficients is obtained. Despite relatively small spin–orbit couplings, it is shown that intersystem crossing is efficient because of multiple passages via long-lived collisional resonances.

The electrochemical reduction of N2 to generate NH3 (NRR) under ambient conditions is a promising alternative to the industrial Haber–Bosch process which requires high temperature and pressure. NRR electrocatalysts are needed to overcome the slow kinetics due to the high energy barrier for NN bond cleavage. Another main challenge is suppressing the competing hydrogen evolution reaction (HER) which results in poor NRR selectivity. Here, we report the development of a novel and cost-efficient electrocatalyst—a phosphotungstic acid (PTA)-supported single metal (M) atom (M-PTA, M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, and Cd) which exhibits substantial stability—via a comprehensive theoretical screening formula of over 20 different d-block metals (M-PTA, M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, and Cd). It is interesting to mention that this class of catalysts has a greatly suppressed HER selectivity with 17 of the 20 candidates falling in the N2-dominant region. Further study demonstrates that Mo-PTA, Tc-PTA and Ru-PTA only demand an energy input of 0.42 eV, 0.24 eV and 0.34 eV for the first hydrogenation step of N2. Detailed analysis of NRR mechanisms show that it follows the distal mechanism with an overpotential of 0.26 V on Mo-PTA. This work provides DFT guidelines for developing stable electrocatalysts through experiments for catalyzing the NRR with high reactivity and selectivity.

The O(3P) + C2H2 reaction is the first step in acetylene oxidation. The accurate kinetic data and the understanding of the reaction dynamics is of great importance. To this end, a full-dimensional global potential energy surface (PES) for the ground triplet state of the O(3P) + C2H2 reaction is constructed based on approximately 85 000 ab initio points calculated at the level of explicitly correlated unrestricted coupled cluster single, double, and perturbative triple excitations with the explicitly correlated polarized valence triple zeta basis set (UCCSD(T)-F12b/VTZ-F12). The PES is fit using the permutation invariant polynomial-neural network (PIP-NN) approach with a total root mean square error of 0.21 kcal mol−1. The key topographic features of the PES, including multiple potential wells and saddle points along different reaction pathways, are well represented by this fit PES. The kinetics and dynamics of the O(3P) + C2H2 reaction are investigated using the quasi-classical trajectory (QCT) method. The calculated rate coefficients are in good agreement with experimental data over a wide temperature range, especially when the temperature is lower than 1500 K. The product branch ratio has also been determined, which indicates the H + HCCO channel as the dominant reaction pathway at 298–3000 K, accounting for 80–90% of the overall rate coefficient, in agreement with experimental observations. The dynamics of the reaction is analyzed in detail.

To provide an in-depth understanding of the HO3 radical and its dissociation to OH + O2, a six-dimensional potential energy surface (PES) has been constructed by fitting 2087 energy points for the electronic ground state of HO3 (X2A′′) using the permutation invariant polynomial-neural network (PIP-NN) approach. The energy points were calculated using an explicitly-correlated and Davidson-corrected multi-reference configuration interaction method with the correlation-consistent polarized valence double zeta basis (MRCI(Q)-F12/VDZ-F12). On the PES, the trans-HO3 isomer is found to be the global minimum, 33.0 cm−1 below the cis-HO3 conformer, which is consistent with previous high-level theoretical investigations. The dissociation to the OH + O2 asymptote from both conformers is shown to be barrierless. As a benchmark from a recently developed high-accuracy thermochemistry protocol, D0 for trans-HO3 is calculated to be 2.29 ± 0.36 kcal mol−1, only slightly deeper than the value of 2.08 kcal mol−1 obtained using the PES, and in reasonable agreement with the experimentally estimated value of 2.93 ± 0.07 kcal mol−1. Using this PES, low-lying vibrational energy levels of HO3 are determined using an exact quantum Hamiltonian and compared with available experimental results.

Ostwald ripening is a key mechanism for sintering of highly dispersed metal nanoparticles in supported catalysts. However, our microscopic understanding of such processes is still primitive. In this work, the atomistic mechanism of the Ostwald ripening of Cu on CeO2(111) is examined via density functional theory calculations. In particular, the detachment of a single Cu atom from ceria supported Cun (n = 2-10, 12, 14, 16, 18, and 20) clusters and trapping on the CeO2(111) surface is investigated in the absence and presence of CO adsorption. It is shown that the adsorption of CO on Cu reduces its detachment energy, which helps in the formation of single atom species on CeO2(111). In addition, the Cu1-CO species is found to diffuse on the CeO2(111) surface with a much lower barrier than a Cu atom. These observations suggest an efficient mechanism for the Ostwald ripening of Cu clusters supported on ceria in the presence of CO. It is further predicted that the Cu1-CO species can eventually migrate to a step site on ceria, generating a stable single-atom motif with a relatively larger binding energy. Finally, the single Cu atom catalyst is shown to possess high activity for the oxygen reduction reaction.

A new and more accurate full-dimensional global potential energy surface (PES) for the ground electronic state of the ClH2O system is developed by fitting 15777 points obtained using an explicitly correlated unrestricted coupled-cluster method with single, double, and perturbative triple excitations (UCCSD(T)-F12b). The fitting is carried out using the permutation invariant polynomial-neural network (PIP-NN) method and has an error of 6.9 meV. The new PES has a slightly lower barrier for the atmospherically important HCl + OH → Cl + H2O reaction than the previous PES based on multi-reference configuration interaction (MRCI) calculations. As a result, it should provide a better characterization of the kinetics. Quantum dynamical calculations of reaction probabilities for both the forward and reverse reactions are performed on this new PES and compared with those on the MRCI PES. They reveal notable differences, resulting apparently from subtle differences in the PESs.

The dissociative chemisorption dynamics of CO on rigid Co(112[combining macron]0) is investigated using a quasi-classical trajectory method on a new global six-dimensional potential energy surface (PES). The PES is fit using a neural network method to represent 24 630 density functional energies in various configurations. The reaction path features deep chemisorption wells and a late barrier for dissociation, agreeing well with previous calculations. The activation energy for dissociation ranges from 0.1 eV at the hollow site to 2.46 eV on the top site, indicating a highly corrugated PES. Effects of the incidence energy of the impinging molecule, its initial orientation, vibrational and rotational excitations, and site specificity are examined. Despite the presence of a low barrier, the initial dissociation probability is very small, even at high incident energies, as a large percentage of trajectories is either trapped or desorbed back to the gas phase. The low reactivity is attributed to inefficient energy transfer into the dissociation reaction coordinate in the chemisorption well where thermal equilibrium is not reached. This system underscores the importance of dynamics in understanding reactions at gas-surface interfaces and in kinetic modeling of catalytic processes.

Cobalt is a widely used catalyst for many heterogeneous reactions, including the Fischer-Tropsch (FT) process, which converts syngas (H2 and CO) to higher hydrocarbons. As a result, a better understanding of the key chemical steps on the Co surface, such as the dissociative chemisorption of H2 as an initial step of the FT process, is of fundamental importance. Here, we report an accurate full-dimensional global potential energy surface for the dissociative chemisorption of H2 on the rigid Co(0001) surface constructed from more than 3000 density functional theory points. The high-fidelity potential energy surface was obtained using the permutation invariant polynomial-neural network method, which preserves both the permutation symmetry of H2 and translational symmetry of the Co(0001) surface. The reaction path features a very low barrier on the top site. Full-dimensional quantum dynamical calculations provide insights into the dissociation dynamics and influence of the initial vibrational, rotational, and orientational degrees of freedom.

Rate constants for the N(4S) + C2(1Σg+) reaction have been measured in a continuous supersonic flow reactor over the range 57 K ≤ T ≤ 296 K by the relative rate technique employing the N(4S) + OH(X2Π) → H(2S) + NO(X2Π) reaction as a reference. Excess concentrations of atomic nitrogen were produced by the microwave discharge method and C2 and OH radicals were created by the in situ pulsed laser photolysis of precursor molecules C2Br4 and H2O2 respectively. In parallel, quantum dynamics calculations were performed based on an accurate global potential energy surfaces for the three lowest lying quartet states of the C2N molecule. The 14A′′ potential energy surface is barrierless, having two deep potential wells corresponding to the NCC and CNC intermediates. Both the experimental and theoretical work show that the rate constant decreases to low temperature, although the experimentally measured values fall more rapidly than the theoretical ones except at the lowest temperatures. Astrochemical simulations indicate that this reaction could be the dominant source of CN in dense interstellar clouds.

The bond selectivity in dissociative chemisorption of HOD on Cu(111) is investigated using a six-dimensional quantum model. It includes all vibrational modes of the impinging molecule on a density functional theory based interaction potential between the molecule and metal surface. It is shown that excitations in the HOD local stretching modes selectively enhance cleavage of the excited bond. This pronounced bond selectivity is attributed to a “late” or “product-like” barrier on the potential energy surface for the dissociative chemisorption and the slow intramolecular vibrational energy redistribution in the water molecule. The existence of mode and bond selectivities also underscores the inadequacy of statistical based transition-state theory in describing this industrially important surface reaction.

Dissociative chemisorption of CH4 on transition-metal surfaces, representing the rate-limiting step in methane steam reforming, has been shown experimentally to be strongly mode selective. To understand the mode selectivity, a twelve-dimensional global potential energy surface is developed for CH4 interacting with a rigid Ni(111) surface based on a large number of density functional theory points. The reaction dynamics is investigated using an eight-dimensional quantum model, which includes representatives of all four vibrational modes of methane. After correcting for surface effects, key experimental observations, including the mode selectivity, are well reproduced. These theoretical results, along with mechanistic analysis, provide insights into this industrially important heterogeneous reaction.

Vesicles and membrane properties play critical roles in reproducing the natural environment of living cells such as nutrient transport and DNA protection. We report how to control the morphology evolutionary stages of the self-assembly of amphiphilic block copolymers composed of hydrophilic–hydrophobic–hydrophilic structure using dissipative particle dynamics method. Two unique intermediate states are obtained by controlling the hydrophobic/hydrophilic block ratio, polymer–solvent interaction, and polymer concentration: (1) bilayer-type membrane such as rod-like, disk-like, or bowl-like micelle (mechanism I), (2) semivesicle originating from the rearranged hydrophilic blocks movement into the center or the trapped hydrophilic blocks during merging (mechanism II). Additionally, during the transition period between these two pathways, vesicles are formed through an in-between pathway. Specifically, instead of the typical mechanism I or mechanism II, hydrophilic blocks gradually diffuse toward the center of some irregular spherical micelles, and then become full vesicles. Most importantly, we show that two factors, the degree of hydrophobicity of the blocks and the probability of the adhesive amphiphile collisions are thought to be of key importance to control the vesicle-formation mechanisms. As a consequence, a crucial balance between the segregation of inner-hydrophobic beads and the attraction of outer-hydrophilic beads drastically affects the self-assembly pathways of amphiphilic block copolymer into vesicles from one mechanism over the other. Furthermore, we demonstrate that when the hydrophilic blocks move toward the center to form a cavity, they can move in randomly and maintain a balanced quantity.

State-to-state differential and integral cross sections for the title reaction were calculated using an exact wave packet method on a recently developed ab initio potential energy surface of the first excited state HO(2)(Ã(2)A'). The calculation results indicate that the reaction is dominated by highly rotationally excited OH products scattered in both the forward and backward directions, consistent with the formation of a long-lived HO(2) reaction intermediate. However, a statistical model was found to overestimate the integral cross sections, due apparently to dynamical bottlenecks. In addition, a unique feature in the OH + O exit channel potential promotes rotational excitation of the departing OH product by exerting a torque force. The role of the title reaction in high temperature combustion is also discussed.

We examine the impact of initial rotational excitation on the reactivity of the H + O(2)--OH + O reaction. Accurate Chebyshev wave packet calculations have been carried out for the upsilon(i) = 0, j(i) = 9 initial state of O(2) and the J = 50 partial wave. In addition, we present Gaussian-weighted quasi-classical trajectory and phase space theory calculations of the integral cross section and thermal rate constant for the title reaction. These theoretical results suggest that the initial rotational excitation significantly enhances reactivity with an amount comparable to the effect of initial vibrational state excitation. The inclusion of internally excited reactants is shown to improve the agreement with experimental rate constant.

Supermolecule density functional theory calculations show that solvent is responsible for the concerted transition state in alkaline hydrolysis of p-nitrophenyl phosphate suggested by heavy atom kinetic isotope effects.