Effects of a single water molecule on the OH + H2O2 reaction

Importance of Spin Channels from Radical-Radical Reactions in Hydrogen-Oxygen Combustion Mechanisms at High Temperatures

Radical-radical reactions can generate two channels with high and low spins. In this work, ten radical-radical reactions with different spin channels and four radical-molecule reactions in hydrogen-oxygen combustion were systematically investigated from a theoretical perspective. The potential energy surface (PES) of radical-radical reactions reveals that the high- and low-spin states of the reactant are energetically degenerate and the two channels are energetically feasible. The difference in rate constants between the high- and low-spin channels gradually decreases as the temperature increases. Then, the kinetic parameters of the 14 bimolecular reactions in the hydrogen-oxygen mechanism of the University of California, San Diego (UCSD), were replaced to simulate the ignition delay time and laminar flame speed. The simulation results agree well with the available experimental findings, indicating the necessity of considering both high- and low-spin channels for kinetic simulation.

Can a single ammonia and water molecule enhance the formation of methanimine under tropospheric conditions?: kinetics of •CH2NH2 + O2 (+NH3/H2O)

The aminomethyl (•CH2NH2) radical is generated from the photo-oxidation of methylamine in the troposphere and is an important precursor for new particle formation. The effect of ammonia and water on the gas-phase formation of methanimine (CH2NH) from the •CH2NH2 + O2 reaction is not known. Therefore, in this study, the potential energy surfaces for •CH2NH2 + O2 (+NH3/H2O) were constructed using ab initio//DFT, i.e., coupled-cluster theory (CCSD(T))//hybrid-density functional theory, i.e., M06-2X with the 6-311++G (3df, 3pd) basis set. The Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) simulation with Eckart's asymmetric tunneling was used to calculate the rate coefficients and branching fractions relevant to the troposphere. The results show 40% formation of CH2NH at the low-pressure (<1 bar) and 100% formation of CH2NH2OO• at the high-pressure limit (HPL) condition. When an ammonia molecule is introduced into the reaction, there is a slight increase in the formation of CH2NH; however, when a water molecule is introduced into the reaction, the increase in the formation of CH2NH was from 40% to ∼80%. The calculated rate coefficient for •CH2NH2 + O2 (+NH3) [1.9 × 10-23 cm3 molecule-1 s-1] and for CH2NH2 + O2 (+H2O) [3.3 × 10-17 cm3 molecule-1 s-1] is at least twelve and six order magnitudes smaller than those for free •CH2NH2 + O2 (2 × 10-11 cm3 molecule-1 s-1 at 298 K) reactions, respectively. Our result is consistent with that of previous experimental and theoretical analysis and in good agreement with its isoelectronic analogous reaction. The work also provides a clear understanding of the formation of tropospheric carcinogenic compounds, i.e., hydrogen cyanide (HCN).

The influence of a single water molecule on the reaction of BrO + HO2

The influence of a single water molecule on the BrO + HO2 hydrogen extraction reaction has been explored by taking advantage of CCSD(T)/aug-cc-pVTZ//B3LYP/6-311 +  + G(d,p) method. The reaction in the absence of water have two distinct kinds of H-extraction channels to generate HOBr + O2 (1Δg) and HBr + O3, and the channel of generation of HOBr + O2 (1Δg) dominated the BrO + HO2 reaction. The rate coefficient of the most feasible channel for the BrO + HO2 reaction in the absence of water is estimated to be 1.44 × 10-11 cm3 molecule-1 s-1 at 298.15 K, which is consistent with the experiment. The introduction of water made the reaction more complex, but the products are unchanged. Four distinct channels, beginning with HO2…H2O with BrO, H2O…HO2 with BrO, BrO…H2O with HO2, H2O…BrO with HO2 are researched. The most feasible channels, stemming from H2O…HO2 with BrO, and BrO…H2O with HO2, are much slower than the reaction of BrO + HO2 without water, respectively. Thus, the existence of water molecule takes a negative catalytic role for BrO + HO2 reaction.

The influence of a single water molecule on the reaction of BrO + HONO

Quantum chemical computations and transition state theory are employed to systematically research the influence of a single molecule water on the BrO + HONO reaction. Two distinct reactions, namely BrO + trans-HONO and BrO + cis-HONO are explored for the reaction in the absence of water, which is mainly decided by the configuration of HONO. With introduction a single water molecule to the reaction, the rate coefficient of the channel starting from BrO + cis-HONO and BrO + trans-HONO are 2.43 × 10^-19 and 5.22 × 10^-22 cm³ molecule^-1 s^-1, which is larger than the reaction in the absence of water. For further comprehend the impact of water on the BrO + HONO reaction, it is necessary to compute the effective rate coefficient by taking into account the concentration of water. The water-assisted effective rate coefficients for the BrO + HONO reaction are smaller than that the reaction in the absence of water. The reaction of BrO with cis-HONO is feasible both in absence and existence of water.

Catalytic Effect of CO2 and H2O Molecules on •CH3 + 3O2 Reaction

The methyl (•CH3) + 3O2 radical is an important reaction in both atmospheric and combustion processes. We investigated potential energy surfaces for the effect of CO2 and H2O molecules on a •CH3+ O2 system. The mechanism for three reaction systems, i.e., for •CH3 + 3O2, •CH3 + 3O2 (+CO2) and •CH3 + 3O2 (+H2O), were explored using ab initio/DFT methods [CCSD(T)//M062X/6-311++G(3df,3pd)] in combination with a Rice−Ramsperger−Kassel−Marcus (RRKM)/master-equation (ME) simulation between a temperature range of 500 to 1500 K and a pressure range of 0.0001 to 10 atm. When a CO2 and H2O molecule is introduced in a •CH3 + 3O2 reaction, the reactive complexes, intermediates, transition states and post complexes become thermodynamically more favorable. The calculated rate constant for the •CH3 + 3O2 (3 × 10−15 cm3 molecule−1 s−1 at 1000 K) is in good agreement with the previously reported experimentally measured values (~1 × 10−15 cm3 molecule−1 s−1 at 1000 K). The rate constant for the effect of CO2 (3 × 10−16 cm3 molecule−1 s−1 at 1000 K) and H2O (2 × 10−17 cm3 molecule−1 s−1 at 1000 K) is at least one–two-order magnitude smaller than the free reaction (3 × 10−15 cm3 molecule−1 s−1 at 1000 K). The effect of CO2 and H2O on •CH3 + 3O2 shows non-RRKM behavior, however, the effect on •CH3 + 3O2 shows RRKM behavior. Our results also demonstrate that a single CO2 and H2O molecule has the potential to accelerate a gas-phase reaction at temperature higher than >1300 K and slow the reaction at a lower temperature. The result is unique and observed for the first time.

The effect of (H2O)n (n = 1-3) clusters on the reaction of HONO with HCl: a mechanistic and kinetic study

The reaction between HONO and HCl is a possible pathway for the generation of ClNO, which is prone to photolyze, produce chlorine radicals, and accelerate the oxidation of tropospheric VOCs. Current experimental and theoretical studies have significant differences in rate constants under similar conditions. This study aims to examine the reasons for this difference. In this study, the effects of a single water molecule, water dimer, water trimer, excess HCl and excess HONO on the reaction mechanism of HONO + HCl were studied at the CCSD(T)/aug-cc-pVTZ//M06-2X/6-311+G(2df,2p) level and the rate constants of each reaction channel were calculated. Our results showed that the reaction potential barrier of HONO with HCl was the lowest only when the water dimer was present, and the reaction rate constants were close to the experimental results, and both the cis-HONO⋯(H₂O)₂ + HCl and the trans-HONO⋯(H₂O)₂ + HCl reaction paths are likely to occur. We think that the reason for the inconsistency between experimental and theoretical results is that the water dimer is involved in the reaction in experiments.

Possible atmospheric source of NH2SO3H: the hydrolysis of HNSO2 in the presence of neutral, basic, and acidic catalysts

NH₂SO₃H can directly participate in H₂SO₄-(CH₃)₂NH-based cluster formation, and thereby substantially enhance the cluster formation rate. Herein, the reaction mechanisms and kinetics for the formation of NH₂SO₃H from the hydrolysis of HNSO₂ without and with neutral (H₂O, (H₂O)₂, and (H₂O)₃), basic (NH₃ and CH₃NH₂), and acidic (HCOOH, H₂SO₄, H₂SO₄⋯H₂O, and (H₂SO₄)₂) catalysts were studied theoretically at the CCSD(T)-F12/cc-pVDZ-F12//M06-2X/6-311+G(2df,2pd) level. The calculated results showed that neutral, basic, and acidic catalysts decrease the energy barrier by over 18.1 kcal mol^-1; meanwhile, the product formation of NH₂SO₃H was more strongly bonded to neutral, basic, and acidic catalysts than to the reactants HNSO₂ and H₂O. This reveals that the reported neutral, basic, and acidic catalysts promote the formation of NH₂SO₃H from the hydrolysis of HNSO₂ both kinetically and thermodynamically. Kinetic calculations using the master equation showed that (H₂O)₂ (100% RH) dominate over the other catalysts within the range of 0-10 km altitudes and 230-320 K with its rate ratio larger by at least 2.98 times, whereas HCOOH (3.2 × 10⁹ molecules cm^-3) is the most favorable catalysts at 15 km altitude in the troposphere. Overall, the present results will provide a definitive example that neutral, basic, and acidic catalysts have important influences on atmospheric reactions.

Effect of Water and Formic Acid on ·OH + CH4 Reaction: An Ab Initio/DFT Study

In this work, we used ab initio/DFT method coupled with statistical rate theory to answer the question of whether or not formic acid (HCOOH) and water molecules can catalyze the most important atmospheric and combustion prototype reaction, i.e., ·OH (OH radical) + CH4. The potential energy surface for ·OH + CH4 and ·OH + CH4 (+X) (X = HCOOH, H2O) reactions were calculated using the combination of hybrid-density functional theory and coupled-cluster theory with Pople basis set [(CCSD(T)/ 6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd)]. The results of this study show that the catalytic effect of HCOOH (FA) and water molecules on the ·OH + CH4 reaction has a major impact when the concentration of FA and H2O is not included. In this situation the rate constants for the CH4 + HO···HCOOH (3 × 10−9 cm3 molecule−1 s−1) reaction is ~105 times and for CH4 + H2O···HO reaction (3 × 10−14 cm3 molecule−1 s−1 at 300 K) is ~20 times higher than ·OH + CH4 (~6 × 10−15 cm3 molecule−1 s−1). However, the total effective rate constants, which include the concentration of both species in the kinetic calculation has no effect under atmospheric condition. As a result, the total effective reaction rate constants are smaller. The rate constants when taking the account of the FA and water for CH4 + HO···HCOOH (4.1 × 10−22 cm3 molecule−1 s−1) is at least seven orders magnitude and for the CH4 + H2O···HO (7.6 × 10−17 cm3 molecule−1 s−1) is two orders magnitude smaller than ·OH + CH4 reaction. These results are also consistent with previous experimental and theoretical studies on similar reaction systems. This study helps to understand how FA and water molecules change the reaction kinetic under atmospheric conditions for ·OH + CH4 reaction.

A computational study of the HO2 + SO3 → HOSO2 + 3O2 reaction catalyzed by water monomer, water dimer and small clusters of sulfuric acid: kinetics and atmospheric implications

Herein, the reaction mechanisms and kinetics for the HO2 + SO3 → HOSO2 + 3O2 reaction catalyzed by water monomer, water dimer and small clusters of sulfuric acid have been...

Effect of a single water molecule on ˙CH2OH + 3O2 reaction under atmospheric and combustion conditions

The hydroxymethyl (˙CH₂OH) radical is an important intermediate species in both atmosphere and combustion reaction systems. The rate coefficients for ˙CH₂OH + ³O₂ and (˙CH₂OH + ³O₂ (+H₂O)) reactions were calculated using the Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) simulation and canonical variational transition state theory (CVT) between the temperature range of 200 to 1500 K based on the potential energy surface constructed using CCSD(T)//ωB97XD/6-311++G(3df,3pd). The results show that ˙CH₂OH + ³O₂ leads to the formation of CH₂O and HO₂ at temperatures below 800 K, and goes back to reactants at high temperature (>1000 K). When a water molecule is added to the reaction, the formation of CH₂O and HO₂ is favored at all temperatures. The calculated rate coefficient for the ˙CH₂OH + ³O₂ (2.8 × 10^-11 cm³ molecule^-1 s^-1 at 298 K) is in good agreement with the previous experimental values (∼1 × 10^-11 cm³ molecule^-1 s^-1 at 298 K). The rate coefficients for the water-assisted reaction (2.4 × 10^-16 cm³ molecule^-1 s^-1 at 1000 K) is at least 3-4 orders of magnitude smaller than the water-free reaction (6.2 × 10^-12 cm³ molecule^-1 s^-1 at 1000 K). This result is consistent with the similar types of reaction system. Our calculations also predict that the effect of a single water molecule favors the formation of CH₂O in the combustion condition. However, the water-free reaction favors the formation of CH₂O in the atmospheric condition. The current study helps to understand how a single water molecule changes the reaction mechanism and chemical kinetic behaviour under atmospheric and combustion conditions.

Effect of ammonia and water molecule on OH + CH3OH reaction under tropospheric condition

The rate coefficients for OH + CH3OH and OH + CH3OH (+ X) (X = NH3, H2O) reactions were calculated using microcanonical, and canonical variational transition state theory (CVT) between 200 and 400 K based on potential energy surface constructed using CCSD(T)//M06-2X/6-311++G(3df,3pd). The results show that OH + CH3OH is dominated by the hydrogen atoms abstraction from CH3 position in both free and ammonia/water catalyzed ones. This result is in consistent with previous experimental and theoretical studies. The calculated rate coefficient for the OH + CH3OH (8.8 × 10-13 cm3 molecule-1 s-1), for OH + CH3OH (+ NH3) [1.9 × 10-21 cm3 molecule-1 s-1] and for OH + CH3OH (+ H2O) [8.1 × 10-16 cm3 molecule-1 s-1] at 300 K. The rate coefficient is at least 8 order magnitude [for OH + CH3OH(+ NH3) reaction] and 3 orders magnitude [OH + CH3OH (+ H2O)] are smaller than free OH + CH3OH reaction. Our calculations predict that the catalytic effect of single ammonia and water molecule on OH + CH3OH reaction has no effect under tropospheric conditions because the dominated ammonia and water-assisted reaction depends on ammonia and water concentration, respectively. As a result, the total effective reaction rate coefficients are smaller. The current study provides a comprehensive example of how basic and neutral catalysts effect the most important atmospheric prototype alcohol reactions.

The favorable routes for the hydrolysis of CH2OO with (H2O)n (n = 1-4) investigated by global minimum searching combined with quantum chemical methods

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.

Atmospheric Chemistry of CH2OO: The Hydrolysis of CH2OO in Small Clusters of Sulfuric Acid

The hydrolysis of CH₂OO is not only a dominant sink for the CH₂OO intermediate in the atmosphere but also a key process in the formation of aerosols. Herein, the reaction mechanism and kinetics for the hydrolysis of CH₂OO catalyzed by the precursors of atmospheric aerosols, including H₂SO₄, H₂SO₄···H₂O, and (H₂SO₄)₂, have been studied theoretically at the CCSD(T)-F12a/cc-pVDZ-F12//B3LYP/6-311+G(2df,2pd) level. The calculated results show that the three catalysts decrease the energy barrier by over 10.3 kcal·mol^-1; at the same time, the product formation of HOCH₂OOH is more strongly bonded to the three catalysts than to the reactants CH₂OO and H₂O, revealing that small clusters of sulfuric acid promote the hydrolysis of CH₂OO both kinetically and thermodynamically. Kinetic simulations show that the H₂SO₄-assisted reaction is more favorable than the H₂SO₄···H₂O- (the pseudo-first-order rate constant being 27.9-11.5 times larger) and (H₂SO₄)₂- (between 2.8 × 10⁴ and 3.4 × 10⁵ times larger) catalyzed reactions. Additionally, due to relatively lower concentration of H₂SO₄, the hydrolysis of CH₂OO with H₂SO₄ cannot compete with the CH₂OO + H₂O or (H₂O)₂ reaction within the temperature range of 280-320 K, since its pseudo-first-order rate ratio is smaller by 4-7 or 6-8 orders of magnitude, respectively. However, the present results provide a good example of how small clusters of sulfuric acid catalyze the hydrolysis of an important atmospheric species.

Oxidation of methane to methanol over Pd@Pt nanoparticles under mild conditions in water

Pd@Pt core–shell colloidal nanoparticles efficiently catalyse the direct oxidation of methane to methanol with high selectivity using H₂O₂ in water.

Ion and radical chemistry in (H2O2)N clusters

We investigate the ionization induced chemistry of hydrogen peroxide in (H₂O₂)_N clusters generated after the pickup of individual H₂O₂ molecules on large free Ar_M, M[combining macron]≈ 160, nanoparticles in molecular beams. Positive and negative ion mass spectra are recorded after an electron ionization of the clusters at energies 5-70 eV and after a slow electron attachment (below 4 eV), respectively. The spectra demonstrate that (H₂O₂)_N clusters with N≥ 20 are formed on argon nanoparticles. This is the first experimental report on hydrogen peroxide clusters in molecular beams. The major negative cluster ion series (H₂O₂)_nO₂^- indicates O₂^- ion formation. The dissociative electron attachment to H₂O₂ molecules in the gas phase yielded only OH^- and O^- (Nandi et al., Chem. Phys. Lett., 2003, 373, 454). These ions and the series containing them are much less abundant in the clusters. We propose a sequence of ion-molecule and radical reactions to explain the formation of O₂^-, HO₂^- and other ions observed in the negatively charged cluster ion series. Since hydrogen peroxide plays an important role in many areas of chemistry from the Earth's atmosphere to biological tissues, our study opens new horizons for experimental investigations of hydrogen peroxide chemistry in complex environments.

Reaction pathways and kinetics study on a syngas combustion system: CO + HO2 in an H2O environment

The reaction between CO and HO2 plays a significant role in syngas combustion. In this work, the catalytic effect of single-molecule water on this reaction is theoretically investigated at the CCSD(T)/aug-cc-pV(D,T,Q)Z and CCSD(T)-F12a/jun-cc-pVTZ levels in combination with the M062X/aug-cc-pVTZ level. Firstly, the potential energy surface (PES) of CO + HO2 (water-free) is revisited. The major products CO2 + OH are formed via a cis- or a trans-transition state (TS) channel and the formation of HCO + O2 is minor. In the presence of water, the title reaction has three different pre-reactive complexes (i.e., RC2: COHO2 + H2O, RC3: COH2O + HO2, and RC4: HO2H2O + CO), depending on the initial hydrogen bond formation. Compared to the water-free process, the reaction barriers of the water-assisted process are reduced considerably, due to more stable cyclic TSs and complexes. The rate constants for the bimolecular reaction pathways CO + HO2, RC2, RC3, and RC4 are further calculated using conventional transition state theory (TST) with Eckart asymmetric tunneling correction. For reaction CO + HO2, our calculations are in good agreement with the literature. In addition, the effective rate constants for the water-assisted process decrease by 1-2 orders of magnitude compared to the water-free one at a temperature below 600 K. In particular, the effective rate constants for the water-assisted and water-free processes are 1.55 × 10-28 and 3.86 × 10-26 cm3 molecule-1 s-1 at 300 K, respectively. This implies that the contribution of a single molecule water-assisted process is small and cannot accelerate the title reaction.

Reaction mechanism, energetics, and kinetics of the water-assisted thioformaldehyde + ˙OH reaction and the fate of its product radical under tropospheric conditions

The reaction of thioformaldehyde with OH radical assisted by a single water molecule in the atmosphere is negligible.

Effect of NH3 and HCOOH on the H2O2 + HO → HO2 + H2O reaction in the troposphere: competition between the one-step and stepwise mechanisms

The H₂O₂ + HO → HO₂ + H₂O reaction is an important reservoir for both radicals of HO and HO₂ catalyzing the destruction of O₃. Here, this reaction assisted by NH₃ and HCOOH catalysts was explored using the CCSD(T)-F12a/cc-pVDZ-F12//M06-2X/aug-cc-pVTZ method and canonical variational transition state theory with small curvature tunneling. Two possible sets of mechanisms, (i) one-step routes and (ii) stepwise processes, are possible. Our results show that in the presence of both NH₃ and HCOOH catalysts under relevant atmospheric temperature, mechanism (i) is favored both energetically and kinetically than the corresponding mechanism (ii). At 298 K, the relative rate for mechanism (i) in the presence of NH₃ (10, 2900 ppbv) and HCOOH (10 ppbv) is respectively 3–5 and 2–4 orders of magnitude lower than that of the water-catalyzed reaction. This is due to a comparatively lower concentration of NH₃ and HCOOH than H₂O which indicates the positive water effect under atmospheric conditions. Although NH₃ and HCOOH catalysts play a negligible role in the reservoir for both radicals of HO and HO₂ catalyzing the destruction of O₃, the current study provides a comprehensive example of how acidic and basic catalysts assisted the gas-phase reactions.

The H₂O₂ + HO → HO₂ + H₂O reaction is an important reservoir for both radicals of HO and HO₂ catalyzing the destruction of O₃.

Atmospheric chemistry of the self-reaction of HO2 radicals: stepwise mechanism versus one-step process in the presence of (H2O)n (n = 1-3) clusters

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.

A single water molecule accelerating the atmospheric reaction of HONO with ClO

The role of a single water molecule on the atmospheric reaction of HONO + ClO is systematically investigated employing quantum chemical calculation combined with harmonic transition state theory. Two reaction pathways, cis-HONO + ClO and trans-HONO + ClO, are identified for the naked reaction, which depends on the configurations of HONO. When adding a single water molecule to this reaction, the rate constants of cis-HONO + ClO and trans-HONO + ClO pathways are 7.97 × 10^-21 and 2.29 × 10^-17 cm³ molecule^-1 s^-1, respectively, larger than the corresponding naked reaction. To further understand the role of water on the HONO + ClO reaction, it is necessary to calculate the effective rate constant by considering the concentration of water. It shows that the effective rate constants of water-assisted cis-HONO + ClO pathway are much smaller than those of the naked reaction, whereas the presence of water accelerates the trans-HONO + ClO at room temperature. This study demonstrates that water has a positive role in the pathway of trans-HONO + ClO by modifying the stabilities of reactant complexes and transition states through the hydrogen bond formation, which contributes to the sink of atmospheric HONO. In addition, the kinetic branching ratio indicates that the favorable reaction is the trans-HONO + ClO instead of the cis-HONO + ClO pathway, in contrast to the naked reaction. These results reveal the importance of water in the evaluation of the fate of active species in the atmosphere. Graphical Abstract.

Role of (H2O) n (n = 1-2) in the Gas-Phase Reaction of Ethanol with Hydroxyl Radical: Mechanism, Kinetics, and Products

The effect of water on the hydrogen abstraction mechanism and product branching ratio of CH₃CH₂OH + ^•OH reaction has been investigated at the CCSD(T)/aug-cc-pVTZ//BH&HLYP/aug-cc-pVTZ level of theory, coupled with the reaction kinetics calculations, implying the harmonic transition-state theory. Depending on the hydrogen sites in CH₃CH₂OH, the bared reaction proceeds through three elementary paths, producing CH₂CH₂OH, CH₃CH₂O, and CH₃CHOH and releasing a water molecule. Thermodynamic and kinetic results indicate that the formation of CH₃CHOH is favored over the temperature range of 216.7-425.0 K. With the inclusion of water, the reaction becomes quite complex, yielding five paths initiated by three channels. The products do not change compared with the bared reaction, but the preference for forming CH₃CHOH drops by up to 2%. In the absence of water, the room temperature rate coefficients for the formation of CH₂CH₂OH, CH₃CH₂O, and CH₃CHOH are computed to be 5.2 × 10^-13, 8.6 × 10^-14, and 9.0 × 10^-11 cm³ molecule^-1 s^-1, respectively. The effective rate coefficients of corresponding monohydrated and dihydrated reactions are 3-5 and 6-8 orders of magnitude lower than those of the unhydrated reaction, indicating that water has a decelerating effect on the studied reaction. Overall, the characterized effects of water on the thermodynamics, kinetics, and products of the CH₃CH₂OH + ^•OH reaction will facilitate the understanding of the fate of ethanol and secondary pollutants derived from it.

Elucidating the mechanism and kinetics of the water-assisted reaction of nitrous acid with hydroxyl radical

The rate constant of the HONO + OH reaction is slightly increased by hydration.

Catalytic effect of (H2O)n (n = 1–3) clusters on the HO2 + SO2 → HOSO + 3O2 reaction under tropospheric conditions

The HO₂ + SO₂ → HOSO + ³O₂ reaction without and with (H₂O)n (n = 1–3) have been investigated using CCSD(T)/CBS//M06-2X/aug-cc-pVTZ methods, and canonical variational transition state theory with small curvature tunneling.

Effects of water, ammonia and formic acid on HO2 + Cl reactions under atmospheric conditions: competition between a stepwise route and one elementary step

Quantum chemical calculations at M06-2X and CCSD(T) levels of theory have been performed to investigate the effects of H₂O, NH₃, and HCOOH on the HO₂ + Cl → HCl + O₂ reaction. The results show that catalyzed reactions with three catalysts could proceed through two different mechanisms, namely a stepwise route and one elementary step, where the former reaction is more favorable than the latter. Meanwhile, for the stepwise route, a single hydrogen atom transfer pathway in the presence of all catalysts has more advantages than the respective double hydrogen atom transfer pathway. Then, the relative impacts of catalysts under tropospheric conditions were investigated by considering the temperature dependence of the rate constants and the altitude dependence of catalyst concentrations. The calculated results show that at 0 km altitude, the HO₂ + Cl → HCl + O₂ reaction with catalysts, such as H₂O, NH₃, or HCOOH, cannot compete with the reaction without a catalyst, as the effective rate constant with a catalyst is smaller by 2–6 orders of magnitude than the naked reaction within the temperature range 280–320 K. The calculated results also show that at altitudes of 5, 10 and 15 km, the effective rate constant of the HCOOH-catalyzed reaction increases obviously with an increase in altitude. At 15 km altitude, its value is up to 9.63 × 10⁻¹¹ cm³ per molecule per s, which is close to the corresponding value of the reaction without a catalyst, showing that the contribution of HCOOH to the HO₂ + Cl → HCl + O₂ reaction cannot be neglected at high altitudes. The new findings in this investigation are not only of great necessity and importance for elucidating the gas-phase reaction of HO₂ with Cl in the presence of acidic, neutral and basic catalysts, but are also of great interest for understanding the importance of other types of hydrogen abstraction in the atmosphere.

The effects of acidic (FA), neutral (WM) and basic (AM) catalysts on the energetic and kinetic aspects of the HO₂ + Cl reaction have been studied. At 298 K, the catalytic order of FA, WM and AM is WM > FA > AM.

The Role of (H₂O)1-2 in the CH₂O + ClO Gas-Phase Reaction

Mechanism and kinetic studies have been carried out to investigate whether one and two water molecules could play a possible catalytic role on the CH₂O + ClO reaction. Density functional theory combined with the coupled cluster theory were employed to explore the potential energy surface and the thermodynamics of this radical-molecule reaction. The reaction proceeded through four different paths without water and eleven paths with water, producing H + HCO(O)Cl, Cl + HC(O)OH, HCOO + HCl, and HCO + HOCl. Results indicate that the formation of HCO + HOCl is predominant both in the water-free and water-involved cases. In the absence of water, all the reaction paths proceed through the formation of a transition state, while for some reactions in the presence of water, the products were directly formed via barrierless hydrogen transfer. The rate constant for the formation of HCO + HOCl without water is 2.6 × 10-16 cm³ molecule-1 s-1 at 298.15 K. This rate constant is decreased by 9-12 orders of magnitude in the presence of water. The current calculations hence demonstrate that the CH₂O + ClO reaction is impeded by water.

Role of water on the H-abstraction from methanol by ClO

The influence of a single water molecule on the reaction mechanism and kinetics of hydrogen abstraction from methanol (CH₃OH) by the ClO radical has been investigated using ab initio calculations. The reaction proceeds through two channels: abstraction of the hydroxyl H-atom and methyl H-atom of CH₃OH by ClO, leading to the formation of CH₃O+HOCl (+H₂O) and CH₂OH+HOCl (+H₂O), respectively. In both cases, pre- and post-reactive complexes were located at the entrance and exit channel on the potential energy surfaces. Results indicate that the formation of CH₂OH+HOCl (+H₂O) is predominant over the formation of CH₃O+HOCl (+H₂O), with ambient rate constants of 3.07×10^-19 and 3.01×10^-23cm³/(molecule·sec), respectively, for the reaction without water. Over the temperature range 216.7-298.2K, the presence of water is seen to effectively lower the rate constants for the most favorable pathways by 4-6 orders of magnitude in both cases. It is therefore concluded that water plays an inhibitive role on the CH₃OH+ClO reaction under tropospheric conditions.

Surface-Enhanced Raman Scattering-Active Substrate Prepared with New Plasmon-Activated Water

Conventionally, reactions in aqueous solutions are prepared using deionized (DI) water, the properties of which are related to inert "bulk water" comprising a tetrahedral hydrogen-bonded network. In this work, we demonstrate the distinguished benefits of using in situ plasmon-activated water (PAW) with reduced hydrogen bonds instead of DI water in electrochemical reactions, which generally are governed by diffusion and kinetic controls. Compared with DI water-based systems, the diffusion coefficient and the electron-transfer rate constant of K₃Fe(CN)₆ in PAW in situ can be increased by ca. 35 and 15%, respectively. These advantages are responsible for the improved performance of surface-enhanced Raman scattering (SERS). On the basis of PAW in situ, the SERS enhancement of twofold higher intensity of rhodamine 6G and the corresponding low relative standard deviation of 5%, which is comparable to and even better than those based on complicated processes shown in the literature, are encouraging.

Therapeutics for Inflammatory-Related Diseases Based on Plasmon-Activated Water: A Review

It is recognized that the properties of liquid water can be markedly different from those of bulk one when it is in contact with hydrophobic surfaces or is confined in nano-environments. Because our knowledge regarding water structure on the molecular level of dynamic equilibrium within a picosecond time scale is far from completeness all of water's conventionally known properties are based on inert "bulk liquid water" with a tetrahedral hydrogen-bonded structure. Actually, the strength of water's hydrogen bonds (HBs) decides its properties and activities. In this review, an innovative idea on preparation of metastable plasmon-activated water (PAW) with intrinsically reduced HBs, by letting deionized (DI) water flow through gold-supported nanoparticles (AuNPs) under resonant illumination at room temperature, is reported. Compared to DI water, the created stable PAW can scavenge free hydroxyl and 2,2-diphenyl-1-picrylhydrazyl radicals and effectively reduce NO release from lipopolysaccharide-induced inflammatory cells. Moreover, PAW can dramatically induce a major antioxidative Nrf2 gene in human gingival fibroblasts. This further confirms its cellular antioxidative and anti-inflammatory properties. In addition, innovatively therapeutic strategy of daily drinking PAW on inflammatory-related diseases based on animal disease models is demonstrated, examples being chronic kidney disease (CKD), chronic sleep deprivation (CSD), and lung cancer.

Effect of a single water molecule on the HO2 + ClO reaction

The catalytic effect of a single water molecule on the HO2 + ClO reaction has been investigated at the CCSD(T)/aug-cc-pVTZ//B3LYP-D3/aug-cc-pVDZ level of theory. Four H-abstraction paths and two kinds of products, among which the paths for HOCl + O2 formation are dominant, have been found for the HO2 + ClO reaction without water. The rate constant of the most favorable path for the reaction without water is computed to be 4.53 × 10-12 cm3 molecule-1 s-1 at room temperature, in good agreement with the experiment. In the presence of a water molecule, although the reaction becomes more complex, the dominant products do not change. Four main channels, starting from HO2H2O + ClO, H2OHO2 + ClO, ClOH2O + HO2 and H2OClO + HO2, are investigated. The most favorable paths, reactions between H2OHO2 and ClO, and between ClOH2O and HO2, are 7-10 and 6-9 orders of magnitude slower than the reaction in the absence of water, respectively. It is concluded that the presence of a single water molecule does not play an important role in enhancing the HO2 + ClO reaction under tropospheric conditions.

Innovatively Therapeutic Strategy on Lung Cancer by Daily Drinking Antioxidative Plasmon-Induced Activated Water

Many human diseases are inflammation-related, such as cancer and those associated with aging. Previous studies demonstrated that plasmon-induced activated (PIA) water with electron-doping character, created from hot electron transfer via decay of excited Au nanoparticles (NPs) under resonant illumination, owns reduced hydrogen-bonded networks and physchemically antioxidative properties. In this study, it is demonstrated PIA water dramatically induced a major antioxidative Nrf2 gene in human gingival fibroblasts which further confirms its cellular antioxidative and anti-inflammatory properties. Furthermore, mice implanted with mouse Lewis lung carcinoma (LLC-1) cells drinking PIA water alone or together with cisplatin treatment showed improved survival time compared to mice which consumed only deionized (DI) water. With the combination of PIA water and cisplatin administration, the survival time of LLC-1-implanted mice markedly increased to 8.01 ± 0.77 days compared to 6.38 ± 0.61 days of mice given cisplatin and normal drinking DI water. This survival time of 8.01 ± 0.77 days compared to 4.62 ± 0.71 days of mice just given normal drinking water is statistically significant (p = 0.009). Also, the gross observations and eosin staining results suggested that LLC-1-implanted mice drinking PIA water tended to exhibit less metastasis than mice given only DI water.

Plasmon-activated water effectively relieves hepatic oxidative damage resulting from chronic sleep deprivation

The role of the hepato-protective agent plasmon-activated water (PAW) as an innovative anti-oxidant during chronic sleep deprivation (SD) is realized in this study. PAW possesses reduced hydrogen-bonded structure, higher chemical potential and significant anti-oxidative properties. In vitro tests using rat liver cell line (Clone-9) have demonstrated that PAW is non-cytotoxic and does not change the cellular migration capacity. The in vivo experiment on SD rats suffering from intense oxidative damage to the liver, an extremely common phenomenon in the present-time with deleterious effects on metabolic function, is performed by feeding PAW to replace deionized (DI) water. Experimental results indicate that PAW markedly reduces oxidative stress with enhanced bioenergetics in hepatocytes. PAW also effectively restores hepatocytic trans-membrane ion homeostasis, preserves membranous structures, and successfully improves liver function and metabolic activity. In addition, the hepato-protective effects of PAW are evidently demonstrated by the reduced values of glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) and the recovery of total protein and albumin levels. With clear evidences of PAW for protecting liver from SD-induced injury, delivering PAW as a powerful hepato-protective agent should be worthy of trailblazing new clinical trials in a healthier, more natural, and more convenient way.

Reactivity of hydropersulfides toward the hydroxyl radical unraveled: disulfide bond cleavage, hydrogen atom transfer, and proton-coupled electron transfer

Hydropersulfides (RSSH) are highly reactive as nucleophiles and hydrogen atom transfer reagents. These chemical properties are believed to be key for them to act as antioxidants in cells. The reaction involving the radical species and the disulfide bond (S-S) in RSSH, a known redox-active group, however, has been scarcely studied, resulting in an incomplete understanding of the chemical nature of RSSH. We have performed a high-level theoretical investigation on the reactions of the hydroxyl radical (˙OH) toward a set of RSSH (R = -H, -CH₃, -NH₂, -C(O)OH, -CN, and -NO₂). The results show that S-S cleavage and H-atom abstraction are the two competing channels. The electron inductive effect of R induces selective ˙OH substitution at one sulfur atom upon S-S cleavage, forming RSOH and ˙SH for the electron donating groups (EDGs), whereas producing HSOH and ˙SR for the electron withdrawing groups (EWGs). The H-Atom abstraction by ˙OH follows a classical hydrogen atom transfer (hat) mechanism, producing RSS˙ and H₂O. Surprisingly, a proton-coupled electron transfer (pcet) process also occurs for R being an EDG. Although for RSSH having EWGs hat is the leading channel, S-S cleavage can be competitive or even dominant for the EDGs. The overall reactivity of RSSH toward ˙OH attack is greatly enhanced with the presence of an EDG, with CH₃SSH being the most reactive species found in this study (overall rate constant: 4.55 × 10¹² M^-1 s^-1). Our results highlight the complexity in RSSH reaction chemistry, the extent of which is closely modulated by the inductive effect of the substituents in the case of the oxidation by hydroxyl radicals.

Mechanistic and kinetic study on the catalytic hydrolysis of COS in small clusters of sulfuric acid

The catalytic hydrolysis of carbonyl sulfide (COS) and the effect of small clusters of H₂O and H₂SO₄ have been studied by theoretical calculations. The addition of H₂SO₄ could increase the enthalpy change (ΔH<0) and decrease relative energy of products (relative energy<0), resulting in hydrolysis reaction changed from an endothermic reaction to an exothermic reaction. Further, H₂SO₄ decreases the energy barrier by 5.25 kcal/mol, and it enhances the catalytic hydrolysis through the hydrogen transfer effect. The (COS + H₂SO₄-H₂O) reaction has the lowest energy barrier of 29.97 kcal/mol. Although an excess addition of H₂O and H₂SO₄ increases the energy barrier, decreases the catalytic hydrolysis, which is consistent with experimental observations. The order of the energy barriers for the three reactions from low to high are as follows: COS + H₂SO₄-H₂O < COS + H₂O + H₂SO₄-H₂O < COS + H₂O+(H₂SO₄)₂. Kinetic simulations show that the addition of H₂SO₄ can increase the reaction rate constants. Consequently, adding an appropriate amount of sulfuric acid promotes the catalytic hydrolysis of COS both kinetically and thermodynamically.

Catalysis and tunnelling in the unimolecular decay of Criegee intermediates

Semi-classical Transition State theory can be applied to catalysed atmospheric reactions, but reaction mode anharmonicity must be treated carefully.

Water catalysis of the reaction between hydroxyl radicals and linear saturated alcohols (ethanol and n-propanol) at 294 K

Water accelerates the title reaction by lowering the energy barrier and increasing the dipole moments of the reactants.

Role of the (H2O)n (n = 1–3) cluster in the HO2 + HO → 3O2 + H2O reaction: mechanistic and kinetic studies

Upon incorporation of the catalyst (H₂O)_n (n = 1–3) into the reaction HO₂ + HO → H₂O + ³O₂, the catalytic effects of water, water dimer, and water trimer mainly arise from the contribution of a single molecule of water vapor.

B, Lin KC. Catalytic effect of a single water molecule on the OH + CH2NH reaction

Effect of water molecule on atmospheric oxidation of imines.