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Molecular simulations of high energetic materials (HEMs) are limited by efficiency and accuracy. Recently, neural network potential (NNP) models have achieved molecular simulations of millions of atoms while maintaining the accuracy of density functional theory (DFT) levels. Herein, an NNP model covering typical HEMs containing C, H, N, and O elements is developed. The mechanical and decomposition properties of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), hexahydro-1,3,5-trinitro-1,3,5-triazine (HMX), and 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20) are determined by employing the molecular dynamics (MD) simulations based on the NNP model. The calculated results show that the mechanical properties of α-RDX, β-HMX, and ε-CL-20 agree with previous experiments and theoretical results, including cell parameters, equations of state, and elastic constants. In the thermal decomposition simulations, it is also found that the initial decomposition reactions of the three crystals are N–NO2 homolysis, corresponding radical intermediates formation, and NO2-induced reactions. This decomposition trajectory is mainly divided into two stages separating from the peak of NO2: pyrolysis and oxidation. Overall, the NNP model for C/H/N/O elements in this work is an alternative reactive force field for RDX, HMX, and CL-20 HEMs, and it opens up new potential for future kinetic study of nitramine explosives. [ABSTRACT FROM AUTHOR]

The hydrolysis reaction of CH2OO with water and water clusters is believed to be a dominant sink for the CH2OO intermediate in the atmosphere. However, the favorable route for the hydrolysis of CH2OO with water clusters is still unclear. Here global minimum searching using the Tsinghua Global Minimum program has been introduced to find the most stable geometry of the CH2OO⋯(H2O)n (n = 1–4) complex firstly. Then, based on these stable complexes, favorable hydrolysis of CH2OO with (H2O)n (n = 1–4) has been investigated using the quantum chemical method of CCSD(T)-F12a/cc-pVDZ-F12//B3LYP/6-311+G(2d,2p) and canonical variational transition state theory with small curvature tunneling. The calculated results have revealed that, although the contribution of CH2OO + (H2O)2 is the most obvious in the hydrolysis of CH2OO with (H2O)n (n = 1–4), the hydrolysis of CH2OO with (H2O)3 is not negligible in atmospheric gas-phase chemistry as its rate is close to the rate of the CH2OO + H2O reaction. The calculated results also show that, in a clean atmosphere, the CH2OO + (H2O)n (n = 1–2) reaction competes well with the CH2OO + SO2 reaction at 298 K when the concentrations of (H2O)n (n = 1–2) range from 20% relative humidity (RH) to 100% RH, and SO2 is 2.46 × 1011 molecules per cm3. Meanwhile, when the RH is higher than 40%, it is a new prediction that the CH2OO + (H2O)3 reaction can also compete well with the CH2OO + SO2 reaction at 298 K. Besides, Born–Oppenheimer molecular dynamics simulation results show that all the favorable channels of the CH2OO + (H2O)n (n = 1–3) reaction cannot react on a time scale of 100 ps in the NVT simulation. However, the NVE simulation results show that the CH2OO + (H2O)3 reaction can be finished well at 8.5 ps, indicating that the gas phase reaction of CH2OO + (H2O)3 is not negligible in the atmosphere. Overall, the present results have provided a definitive example of how the favorable hydrolysis of important atmospheric species with (H2O)n (n = 1–4) takes place, which will stimulate one to consider the favorable hydrolysis of water and water clusters with other Criegee intermediates and other important atmospheric species. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations at B3LYP and CCSD(T) levels have been performed to investigate the effects of X (X = H2O, (H2O)2, NH3, and H3N···H2O) on HNO3 formation by the direct (HO2 + NO → HNO3) and indirect (N2O4 + H2O → HONO + HNO3) reaction of HO2 + NO. The results show that, for the direct H2O‐assisted reaction, the entrance of H2O···HO2 and NO is more important than the three other channels of HO2···H2O + NO, H2O···NO + HO2, and NO···H2O + HO2. In the H2O···HO2 + NO reactions, (H2O)2, NH3, and H3N···H2O have also been taken into account and substituted in place of H2O; however, their contributions are negligible compared with the H2O···HO2 + NO reaction. It is noted that the atmospheric gas‐phase reaction of H2O···HO2 + NO is not only competitive with the HO2 + NO2 → HNO3 reaction but can also compete well with the NO2 + HO reaction during the day and night at 298 K. Unlike the direct reaction assisted by X, the catalytic effect taken from X can be neglected in the indirect reaction of N2O4 + H2O → HONO + HNO3. However, theoretical results of the direct and indirect reaction of HO2 + NO above may be the main reason why the yield of HNO3 formation in HO2 + NO reaction increases experimentally in the presence of water. [ABSTRACT FROM AUTHOR]

A detailed theoretical study on the reaction mechanisms for the formations of H2O2 + 3O2 from the self‐reaction of HO2 radicals under the effect of NH3, H3N···H2O, and H2SO4 catalysts was performed using the CCSD(T)/CBS//M06‐2X/aug‐cc‐pVTZ method. The rate constant was computed using canonical variational transition state theory (CVT) with small curvature tunneling (SCT). Our results indicate that NH3‐, H3N···H2O‐, and H2SO4‐catalyzed reactions could proceed through both one‐step and stepwise routes. Calculated rate constants show that the catalyzed routes in the presence of the three catalysts all prefer stepwise pathways. Compared to the catalytic efficiency of H2O, the efficiencies of NH3, H3N···H2O, and H2SO4 are much lower due to their smaller relative concentrations. The present results have provided a definitive example of how basic and acidic catalysts influence the atmospheric reaction of HO2 + HO2 → H2O2 + 3O2. These results further encourage one to consider the effects of basic and acidic catalysts on the related atmospheric reactions. Thus, the present investigation should have broad implications in the gas‐phase reactions of the atmosphere. [ABSTRACT FROM AUTHOR]

The addition reaction of CH2OO + H2S → HSCH2OOH without and with catalyst X (X = H2O and (H2O)2) has been investigated by CCSD(T)-F12a/VTZ-F12//B3LYP/aug-cc-pVTZ method and canonical variational transition state theory with small curvature tunneling correction. When H2O was introduced in the CH2OO + H2S reaction, it not only acts as a catalyst for producing HSCH2OOH, but also plays as a reactant to forming HOCH2OOH. The formation channel of HSCH2OOH is more important than the formation channel of HOCH2OOH with its calculated rate constant larger by 11.0–43.2 times within the temperature 280–320 K. Then, (H2O)2 catalysed CH2OO + H2S → HSCH2OOH reaction has been taken into account with its rate lower 1.9–4.2 times than the reaction of CH2OO + H2S → HSCH2OOH with water. Also, CH2OO + H2S with H2O cannot compete with the CH2OO + H2S reaction without water. This is different from CH2OO + (H2O)2 reaction, which is about 4 orders of magnitude larger than the rate constant for CH2OO + H2O reaction. Such discrepancy is possible because C(CH2OO)···O(H2O) interaction has been enhanced more obviously by H2O as compared to that of C(CH2OO)···O(H2S) interaction. [ABSTRACT FROM AUTHOR]

A detailed effects of catalyst X (X = H2O, (H2O)2, NH3, NH3···H2O, H2O···NH3, HCOOH and H2SO4) on the HO4H → O3 + H2O reaction have been investigated by using quantum chemical calculations and canonical vibrational transition state theory with small curvature tunnelling. The calculated results show that (H2O)2-catalysed reactions much faster than H2O-catalysed one because of the former bimolecular rate constant larger by 2.6–25.9 times than that of the latter one. In addition, the basic H2O···NH3 catalyst was found to be a better than the neutral catalyst of (H2O)2. However it is marginally less efficient than the acidic catalysts of HCOOH, and H2SO4. The effective rate constant (k't) in the presence of catalyst X have been assessed. It was found from k't that H2O (at 100% RH) completely dominates over all other catalysts within the temperature range of 280–320 K at 0 km altitude. However, compared with the rate constant of HO4H → H2O + O3 reaction, the keff values for H2O catalysed reaction are smaller by 1–2 orders of magnitude, indicating that the catalytic effect of H2O makes a negligible contribution to the gas phase reaction of HO4H → O3 + H2O. Highlights A detailed effects of catalyst of H2O, (H2O)2, NH3, NH3···H2O, H2O···NH3, HCOOH and H2SO4 on the HO4H → O3 + H2O reaction has been performed. From energetic viewpoint, H2SO4 exerts the strongest catalytic role in HO4H → O3 + H2O reaction as compared with the other catalysts. At 0 km altitude H2O (at 100% RH) completely dominates over all other catalysts within the temperature range of 280–320 K. HO4H → H2O + O3 reaction with H2O cannot be compete with the reaction without catalyst, due to the fact that the effective rate constants in the presence of H2O are smaller. [ABSTRACT FROM AUTHOR]

The effects of water on radical–radical reactions are of great importance for the elucidation of the atmospheric oxidation process of free radicals. In the present work, the HO2 + HO2 reactions with (H2O)n (n = 1–3) have been investigated using quantum chemical methods and canonical variational transition state theory with small curvature tunneling. We have explored both one-step and stepwise mechanisms, in particular the stepwise mechanism initiated by ring enlargement. The calculated results have revealed that the stepwise mechanism is the dominant one in the HO2 + HO2 reaction that is catalyzed by one water molecule. This is because its pseudo-first-order rate constant (kRWM1′) is 3 orders of magnitude larger than that of the corresponding one-step mechanism. Additionally, the value of kRWM1′ at 298 K has been found to be 4.3 times larger than that of the rate constant of the HO2 + HO2 reaction (kR1) without catalysts, which is in good agreement with the experimental findings. The calculated results also showed that the stepwise mechanism is still dominant in the (H2O)2 catalyzed reaction due to its higher pseudo-first-order rate constant, which is 3 orders of magnitude larger than that of the corresponding one-step mechanism. On the other hand, the one-step process is much faster than the stepwise mechanism by a factor of 105–106 in the (H2O)3 catalyzed reaction. However, the pseudo-first-order rate constants for the (H2O)2 and (H2O)3-catalyzed reactions are lower than that of the H2O-catalyzed reaction by 3–4 orders of magnitude, which indicates that the water monomer is the most efficient one among all the catalysts of (H2O)n (n = 1–3). The present results have provided a definitive example that water and water clusters have important influences on atmospheric reactions. [ABSTRACT FROM AUTHOR]

The singlet and triplet reaction mechanisms and rate constants for CH3CH2O + HO2 and CH3CHOH + HO2 reactions were investigated by employing the high‐level quantum chemical calculations with CBS‐QB3 theoretical method and conventional transition state theory with the Wigner tunneling correction. For CH3CH2O + HO2 reaction, four direct hydrogen abstraction processes and five addition‐elimination channels were identified, while two direct hydrogen abstraction routes and nine addition‐elimination channels were found in CH3CHOH + HO2 reaction. The results show that the triplet addition‐elimination channels of CH3CH2OH + 3O2 and CH3COOH + H2O are, respectively, the most favorable channels for CH3CH2O + HO2 and CH3CHOH + HO2 reactions. This is because that they have lower energy barrier and their contribution to the overall rate constants are, respectively, 57% to 86% and 44% to 80%. This work may lead to a better understanding of the mechanism and the kinetic for the singlet and triplet reactions of CH3CH2O + HO2 and CH3CHOH + HO2. Direct hydrogen abstraction routes and addition‐elimination channels were found in CH3CH2O + HO2 and CH3CHOH + HO2 reactions. Triplet addition‐elimination channels of CH3CH2OH + 3O2 and CH3COOH + H2O are, respectively, the most favorable channels for CH3CH2O + HO2 and CH3CHOH + HO2 reactions. In the calculated temperature range, the rate constants of the major channels all decrease with temperature increase. [ABSTRACT FROM AUTHOR]