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The experimental observation of hydroxymethylene, HCOH, following excitation of methanol at 193 nm, was reported recently (Hockey, E. K.; McLane, N.; Martí, C.; Duckett, L.; Osborn, D. L.; Dodson, L. G. Direct Observation of Gas-Phase Hydroxymethylene: Photoionization and Kinetics Resulting from Methanol Photodissociation. J. Am. Chem. Soc. 2024, 146, 14416-14421, 10.1021/jacs.4c03090). This stimulated us to investigate a dynamic mechanism for its formation using a global potential energy surface for the ground electronic state (S 0 ) of methanol. We show via quasi-classical trajectory calculations that hydroxymethylene is indeed formed under the reasonable assumption that the initially excited state undergoes rapid internal conversion to S 0 . From the trajectories, fractional yields of the six major product channels are determined as a function of excitation energy, and the rate of production of each is determined from the fractions and rate of methanol disappearance. Roaming is observed in trajectories leading to the OH and CH 3 products as well as in those leading to CH 2 OH + H and non-reactive trajectories. A "frustrated" roaming accounts for roughly 20% of the HCOH production.

Akin to the traditional quasi-classical trajectory method for investigating the dynamics on a single adiabatic potential energy surface for an elementary chemical reaction, we carry out the dynamics on a 2-state ab initio potential energy surface including nonadiabatic coupling terms as friction terms for D + + H 2 collisions. It is shown that the resulting dynamics correctly accounts for nonreactive charge transfer, reactive non-charge transfer and reactive charge transfer processes. In addition, it leads to the formation of triatomic DH 2 + species as well.

The hydrogen abstraction reaction of OH + CH 3 OH plays a great role in combustion and atmospheric and interstellar chemistry and has been extensively studied theoretically and experimentally. Theoretically, the numerical gradients with respect to the Cartesian coordinates of atoms in molecular simulations on our recent potential energy surface (PES) for the title reaction trained using the permutationally invariant polynomial neural network (PIP-NN) approach hinder the extensive calculation because of the unaffordable computation cost. To address this issue, we in this work report a new full-dimensional accurate analytical PES for the title reaction using the fundamental invariant neural network (FI-NN) approach based on 140,192 points of the quality UCCSD(T)-F12a/AVTZ. Besides, the spin-orbit (SO) corrections of OH in the entrance channel were determined at the level of complete active space self-consistent field with the AVTZ basis set. As a compromise between computational cost and efficiency, the Δ-machine learning approach was employed to construct the SO-corrected PES. Based on this new FI-NN PES with analytical forces, thermal rate coefficients and various dynamic properties, including the integral cross sections, the differential cross sections, and the product energy partitioning, were determined by running a total of 5.5 million trajectories. The use of analytical gradients of the FI-NN PES accelerated simulations and about 99% of computation cost was saved, compared to that for the PIP-NN PES with numerical gradients. Such a significant acceleration is achieved mainly by replacing PIPs with FIs.

The ultracold reaction offers a unique opportunity to elucidate the intricate microscopic mechanism of chemical reactions, and the Na 2 Li system serves as a pivotal reaction system in the investigation of ultracold reactions. In this work, a high-precision potential energy surface (PES) of the Na 2 Li system is constructed based on high-level ab initio energy points and the neural network (NN) method, and a proper asymptotic functional form is adopted for the long-range interaction, which is suitable for the study of cold or ultracold collisions. Based on the new NN PES, the dynamics of the Li + Na 2 ( v = 0, j = 0) → Na + NaLi reaction are studied in the collision energy range of 10 -7 to 80 cm -1 . In the high collision energy range of 8 to 80 cm -1 , the dynamics of the reaction is studied using the time-dependent wave packet method and the statistical quantum mechanical (SQM) method. Comparing the results of the two methods, it is found that the SQM method provides a rough description of the product ro-vibrational state distribution but overestimates the integral cross-section values. With the decrease of collision energy, the reaction differential cross section gradually changes from forward-backward symmetric scattering to predominant forward scattering. In the low collision energy range from 10 -7 to 8 cm -1 , the SQM method is used to study the reaction dynamics, and the rate constant in the Wigner threshold region is estimated to be 2.87 × 10 -10 cm 3 /s.

The reactive collision between Ca and H 2 molecules has attracted great interest experimentally due to the key role of the product CaH molecule in the field of astrophysics and cold molecules. However, quantum dynamics calculations for this system have not been reported due to the lack of a global potential energy surface (PES). Herein, a globally accurate PES of the ground-state CaH 2 is developed by combining 11365 high-level ab initio points and permutation invariant polynomial neural network method. Based on the newly constructed PES, the state-to-state quantum dynamics calculations for the Ca( 1 S) + H 2 ( v 0 = 0, j 0 = 0) → CaH + H reaction are carried out using the time-dependent wave packet method. The dynamic results reveal that the reaction follows the complex-forming mechanism near the reactive threshold, whereas both the indirect insertion mechanism and direct abstraction mechanism have effects at higher collision energies. The newly constructed PES can be used to further study the influence of isotope substitution, rovibrational excitation, and spatial orientation of reactant molecules on reaction dynamics., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

We report a full-dimensional ab initio analytical potential energy surface (PES), which accurately describes the HCl + C 2 H 5 multichannel reaction. The new PES is developed by iteratively adding selected configurations along HCl + C 2 H 5 quasi-classical trajectories (QCTs), thereby improving our previous Cl( 2 P 3/2 ) + C 2 H 6 PES using the Robosurfer program package. QCT simulations for the H'Cl + C 2 H 5 reaction reveal hydrogen-abstraction, chlorine-abstraction, and hydrogen-exchange channels leading to Cl + C 2 H 5 H', H' + C 2 H 5 Cl, and HCl + C 2 H 4 H', respectively. Hydrogen abstraction dominates in the collision energy ( E coll ) range of 1-80 kcal/mol and proceeds with indirect isotropic scattering at low E . Chlorine abstraction opens around 40 kcal/mol collision energy and becomes competitive with hydrogen abstraction at coll and forward-scattered direct stripping at high E coll for both abstraction reactions, and in the case of the HCl reactant, H/Cl-side preference for the H/Cl abstraction. For hydrogen abstraction, the collision energy transfer into the product translational and internal energy is almost equally significant, whereas in the case of chlorine abstraction, most of the available energy goes into the internal degrees of freedom. Hydrogen exchange is a minor channel with nearly constant reactivity in the E coll = 80 kcal/mol. A restricted opening of the cone of acceptance in the Cl-abstraction reaction is found to result in the preference for a backward-scattering direct-rebound mechanism at all energies studied. Initial attack-angle distributions show mainly side-on collision preference of C 2 H 5 for both abstraction reactions, and in the case of the HCl reactant, H/Cl-side preference for the H/Cl abstraction. For hydrogen abstraction, the collision energy transfer into the product translational and internal energy is almost equally significant, whereas in the case of chlorine abstraction, most of the available energy goes into the internal degrees of freedom. Hydrogen exchange is a minor channel with nearly constant reactivity in the E coll range of 10-80 kcal/mol.

The reaction of H + Cl 2 → HCl + Cl plays a crucial role in various fields. However, no previous study has investigated this reaction using accurate quantum mechanical methods. In this paper, we construct a global potential energy surface (PES) using the neural network method with more than 20,000 ab initio energies obtained by the MRCI-F12+Q method with the aug-cc-pV5Z basis and extrapolated to the complete basis set limit. The spin-orbit coupling of the Cl atom has been considered in the PES. With this new PES, product state-resolved quantum dynamics calculations for the H + Cl 2 ( v 0 = 0, j 0 = 0-2) → HCl + Cl reaction was carried out. Numerical results show that the initial rotational excitation of the Cl 2 has negligible effects on the reactivity. Product state-resolved integral cross sections (ICS) and rate constants reveal that the HCl is most favorably produced in its v ' = 2 vibrational state. The calculated product vibrational state-resolved and total reaction rate constants suggest that the new global PES is accurate enough, as compared with the available experimental measurements.

The study of ultrafast photoinduced dynamics of adsorbates on metal surfaces requires thorough investigation of laser-excited electrons and, in many cases, the highly excited surface lattice. While ab initio molecular dynamics with electronic friction and thermostats ( T e )-AIMDEF addresses such complex modeling, it imposes severe computational costs, hindering quantitative comparison with experimental desorption probabilities. In order to bypass this limitation, we utilize the embedded atom neural network method to construct a potential energy surface (PES) for the coadsorption of CO and O on Ru(0001). Our results demonstrate that this PES not only reproduces the short-time ab initio dynamics but is also able to yield statistically significant data for long lasting trajectories that correlate well with experimental findings. Furthermore, the analysis of the laser-induced dynamics reveals the existence of a dynamic trapping state that acts as a precursor for CO desorption, and it is not observed under thermal conditions. Altogether, our results validate the underlying theoretical framework, providing robust support for the description of not only the photoinduced desorption but also the oxidation of CO in terms of nonequilibrated but thermal hot electrons and phonons.T l )-AIMDEF addresses such complex modeling, it imposes severe computational costs, hindering quantitative comparison with experimental desorption probabilities. In order to bypass this limitation, we utilize the embedded atom neural network method to construct a potential energy surface (PES) for the coadsorption of CO and O on Ru(0001). Our results demonstrate that this PES not only reproduces the short-time ab initio dynamics but is also able to yield statistically significant data for long lasting trajectories that correlate well with experimental findings. Furthermore, the analysis of the laser-induced dynamics reveals the existence of a dynamic trapping state that acts as a precursor for CO desorption, and it is not observed under thermal conditions. Altogether, our results validate the underlying theoretical framework, providing robust support for the description of not only the photoinduced desorption but also the oxidation of CO in terms of nonequilibrated but thermal hot electrons and phonons., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

We constructed a new ab initio potential energy surface (PES) for CO-N 2 O which includes the intramolecular Q 3 normal coordinate for the N 2 antisymmetric stretching vibration. The intermolecular potential was evaluated employing the supermolecular method at the [CCSD(T)]-F12a level, with the aug-cc-pVTZ basis set plus bond functions. By integral over the intramolecular 3 antisymmetric stretching vibration. The intermolecular potential was evaluated employing the supermolecular method at the [CCSD(T)]-F12a level, with the aug-cc-pVTZ basis set plus bond functions. By integral over the intramolecular Q 3 coordinate, we obtained the vibrationally averaged PESs for the CO-N 2 O system in the ground and ν 3 O, the radial discrete variable representation/angle finite base representation method and the Lanczos algorithm were applied for the calculations of bound states and rovibrational energy levels. The calculated ν 2 O. Each PES features one nearly T-shaped global minimum and one skewed T-shaped local minimum. Based on these obtained PESs of CO-N 2 O, the radial discrete variable representation/angle finite base representation method and the Lanczos algorithm were applied for the calculations of bound states and rovibrational energy levels. The calculated ν 3 vibrational band origin shift of the N 2 O monomer in CO-N 2 O is 2.7570 cm -1 , matching well with the observed value of 2.9048 cm -1 . The computed microwave and infrared transition frequencies, as well as the rotational parameters, are consistent with the experimental observations.

As the most abundant molecule in the universe, collisions involving H 2 have important implications in astrochemistry. Collisions between hydrogen molecules also represent a prototype for assessing various dynamic methods for understanding fundamental few-body processes. In this work, we develop a new and highly accurate full-dimensional potential energy surface (PES) covering all reactive channels of the H 2 + H 2 system, which extends our previously reported H 2 + H 2 nonreactive PES [J. Chem. Theory Comput., 2021, 17, 6747] by adding 39,538 additional ab initio points calculated at the MRCI/AV5Z level in the reactive channels. The global PES is represented with high fidelity (RMSE = 0.6 meV for a total of 79,000 points) by a permutation invariant polynomial neural network (PIP-NN) and is suitable for studying collision-induced dissociation, single-exchange, as well as four-center exchange reactions. Preliminary quasi-classical trajectory studies on the new PIP-NN PES reveal strong vibrational enhancement of all reaction channels.

We report a full dimensional ab initio potential energy surface for NaCl-H 2 based on precise fitting of a large data set of CCSD(T)/aug-cc-pVTZ energies. A major goal of this fit is to describe the very long-range interaction accurately. This is done in this instance via the dipole-quadrupole interaction. The NaCl dipole and the H 2 quadrupole are available through previous works over a large range of internuclear distances. We use these to obtain exact effect charges on each atom. Diffusion Monte Carlo calculations are done for the ground vibrational state using the new potential.

H 2 O-H 2 is a prototypical five-atom van der Waals system, and the interaction between H 2 O and H 2 plays an important role in many physical and chemical environments. However, previous full-dimensional intermolecular potential energy surfaces (IPESs) cannot accurately describe the H 2 O-H 2 interaction in the repulsive or van der Waals minimum region. In this work, we constructed a full-dimensional IPES for the title system with a small root-mean-square error of 0.252 cm -1 by using the permutation invariant polynomial neural network method. The ab initio calculations were performed by employing the explicitly corrected coupled cluster [CCSD(T)-F12a] method with the augmented correlation-consistent polarized valence quintuple-ζ basis set. Based on the newly developed IPES, the bound states of the H 2 O-H 2 complex were calculated within the rigid-rotor approximation. The transition frequencies and band origins agreed well with the experimental values [Weida, M. J.; Nesbitt, D. J. J. Chem. Phys. 1999 , 110, 156-167] with errors less than 0.1 cm -1 for most transitions. Those results demonstrate the high accuracy of our new IPES, which would build a solid foundation for the collisional dynamics of H 2 O-H 2 at low temperatures.

The high dimensional machine learning potential (MLP) that has developed rapidly in the past decade represents a giant step forward in large-scale atomic simulation for complex systems. The long-range interaction and the poor description of chemical reactions are typical problems of high dimensional MLP, which are mainly caused by the poor structure discrimination of the atom-centered ML model. Herein, we propose a low-cost neural-network-based MLP architecture for fitting global potential energy surface data, namely, G-MBNN, that can offer improved energy and force resolution on a complex potential energy surface. In G-MBNN, a set of many-body energy terms based on the local atomic environment are explicitly included in computing the total energy─the total energy of the system is written as the sum of atomic energy and many-body energy contributions. These extra many-body energy terms are computationally low-cost and, importantly, can provide easy access to delicate energy terms in complex systems such as very short repulsion, long-range attractions, and sensitive angular-dependent covalent interactions. We implement G-MBNN in the LASP code and demonstrate the improved accuracy of the new framework in representative systems, including ternary-element energy materials LiCoO x , TiO 2 with defects, and a series of organic reactions.

Theoretical studies of the potential energy surface and vibrational bound states calculations were performed for the ground state of the Ne-Li 2 + ( X 2 Σ g + ) van der Waals (vdW) complex. The intermolecular interactions were investigated by using an accurate monoconfigurational RCCSD( T ) method and large basis sets (aug-cc-pVnZ, n ) system through nuclear quantum calculations. By studying the aspect of the potential energy surface, the analysis sheds light on the behavior of the Ne-Li 2 + ( X 2 Σ g + ) system through nuclear quantum calculations. By studying the aspect of the potential energy surface, the analysis sheds light on the behavior of the Ne-Li 2 + ( X 2 Σ g + ) complex and its interactions between repulsive and attractive forces with other particles. By examining the vibrational states and wave functions of the system, the researchers were able to gain a better understanding of the behavior of the Ne-Li 2 + ( X 2 Σ g + ) complex. The calculated radial and angular distributions for all even and odd symmetries are discussed in detail. We observe that the radial distributions exhibit a more complicated nodal structure, representing stretching vibrational behavior in the neon atom along its radial coordinate. For the highest bound states, the situation is very different, and the energies surpass the angular barrier.

The CH 2 OO + H 2 O reaction is an important atmospheric process that leads to the formation of formic acid (HCOOH) and water via the intermediate hydroxymethyl hydroperoxide (HOCH 2 OOH, HMHP). We investigated the intricacies of this process by employing quasiclassical trajectory calculations on an accurate, full-dimensional ab initio potential energy surface (PES). In addition to the direct mechanism via the transition state (TS), an interesting roaming mechanism was found to play the predominant role in producing H 2 O and HCOOH. This roaming pathway is featured as the near direct dissociation of HMHP into OH and hydroxymethoxy radical, followed by the retraction of OH and abstraction of the H atom, culminating in the formation of H 2 O. Due to the longer interaction time of the roaming mechanism, less product translational energy was released, but more internal energies of HCOOH were obtained, as compared with the direct TS mechanism. The enhanced yield of H 2 O and formic acid achieved through roaming dynamics underscores the significance of dynamics simulations based on an accurate full-dimensional PES. This work provides new insights into the dynamics of the CH 2 OO + H 2 O reaction and its implications for atmospheric chemistry.