ClO Reaction Research Articles

Stress corrosion cracking of 1Cr17Ni2 countersunk screw during the COVID-19 epidemic prevention

In the construction of the aircraft, countersunk screws are the preferred fasteners. While during the COVID-19 epidemic prevention, the screws suffered fracture after short service. Results indicated that the SCC susceptibility of screw increased in the K2CO3 and 84-disinfectant environment. The screw exhibited brittle fracture in the 84-disinfectant environment, characterized as necking free and more cleavage planes. The rapid fracture of screw occurred in the 84-disinfectant environment, whether under constant of 12000 N or 20000 N. The screw was significantly degraded during 84-disinfectant dripping-salt spray cyclic test. The corrosion current density increased and the passivation almost disappeared in the 84-disinfectant environment. The SCC mechanism of screw is dominated by the strong oxidation of 84-disinfectant, caused by the cathodic reaction of ClO-. Moreover, the interaction at the bottom of the cross groove between the corrosion dissolution and the stress distribution is clarified by the mechanochemistry.

A Chitosan-Based Fluorescent Probe Combined with Smartphone Technology for the Detection of Hypochlorite in Pure Water.

Using chitosan as a raw material, 1,8-naphthimide as the fluorescent chromophore, and sulfur-containing compounds as the recognition groups, a novel naphthimide-functionalized chitosan probe, CS-BNS, for the detection of ClO- was successfully synthesized. The modification of chitosan was verified by SEM, XRD, FTIR, mapping, 13C-NMR, TG and the structure of the probe molecule was characterized. The identification performance of the probes was studied using UV and fluorescence spectrophotometers. The results show that CS-BNS exhibits a specific response to ClO- based on the oxidative reaction of ClO- to the recognition motifs, as well as a good resistance to interference. And the probe has high sensitivity and fast response time, and can complete the detection of ClO- in a pure water system within 60 s. The probe can also quantify ClO- (y = 30.698x + 532.37, R2 = 0.9833) with a detection limit as low as 0.27 μM. In addition, the combination of the probe with smartphone technology enables the visualization and real-time monitoring of ClO-. Moreover, an identification system for ClO- was established by combining the probe with smartphone technology, which realized the visualization and real-time monitoring of ClO-.

HONO Formation from the Oxidation Reactions of ClO, NO, and Water in the Gas-Phase and at the Air-Water Interface

Nitrous acid (HONO) plays a key role in atmospheric chemistry. Nevertheless, the HONO formation mechanism in the atmosphere, especially in the marine boundary layer, remains to be fully understood. Here, Born–Oppenheimer molecular dynamic and metadynamics simulations were performed to study the formation mechanism of HONO from the oxidation reactions of ClO radical and NO with the addition of (H2O)1–2, considering a monohydrated system ((ClO)(NO)(H2O)1) and dihydrated system ((ClO)(NO)(H2O)2), as well as at the air-water interface. This study shows that HONO formation follows a single-water mechanism in gas-phase and air-water interface systems. The free-energy barrier of the (ClO)(NO)(H2O)1 system was 9.66 kJ mol−1, whereas the (ClO)(NO)(H2O)2 system was a barrierless reaction. HONO formation at the air-water interface was faster than that in monohydrated and dihydrated systems. Although the concentration of ClO radical in the marine boundary layer is two orders higher than that of Cl radical, the production rates of HONO from the (ClO)(NO)(H2O)1 system are six orders lower than that from the (Cl)(NO)(H2O)1 system, which means that Cl radical dominates HONO formation rather than ClO radical in the marine boundary layer. These results can deepen our understanding of the HONO formation mechanism and be used to reduce HONO emissions and establish HONO-control strategies.

Chlorate induced false reduction in chemical oxygen demand (COD) based on standard dichromate method: Countermeasure and mechanism

Deliberate addition of mildly oxidative chlorate (ClO3−), so-called “chemical oxygen demand (COD) remover”, into wastewater in China or electrochemical production of ClO3− from Cl− induces the false COD reduction, which would bring about false appearance of effluents meeting the COD discharge standards. In this study, an easy sulfite-based reduction method was developed for the first time to remove ClO3− from the water samples before COD determination to eliminate this interference of ClO3−. In this reaction system, keeping the reaction temperature of sulfite reducing ClO3− at 60 °C was crucial for fast ClO3− removal rate, fixed molar [sulfite]ini/[chlorate]ini ratio value and the synchronous exhaustion of sulfite and ClO3−, which were of great significance for the real application of this improved COD determination method. The ClO3− interference on COD determination could be successfully eliminated after 20 min reduction of ClO3− by sulfite at pHini 4.0∼6.0 with the molar [sulfite]ini/[chlorate]ini ratio value in the range of 5∼6 when concentration of ClO3− was below 5 mM. Despite of the involvement of SO4·− in the sulfite reducing ClO3− system, the degradation of organic matters by SO4·− could be greatly impeded due to the lessened dissolved oxygen for SO4·− production at high reaction temperature and the scavenging of SO4·− by sulfite. In this reaction system, ClO2, ClO2− and ClO− were also generated and could be further reduced by sulfite stoichiometrically via oxygen transfer process with Cl− as the final product. In general, this study pioneered an effective, fast and convenient method for COD determination of the ClO3−-laden wastewaters and evaluating the real electrochemical wastewater treatment performance in terms of COD removal.

Ab initio study of the mechanism of the reaction ClO + O --> Cl + O2

Abstract. Ab initio investigation on the reaction mechanism of ClO + O --> Cl + O2 reaction has been performed using correlation consistent triple zeta basis set. The geometry and frequency of the reactants, products, minimum energy geometries and transition states are obtained using MP2 method and energetics are obtained at the QCISD(T)//MP2 level of theory. Primarily, a possible reaction mechanism is obtained on the basis on IRC calculations using MP2 level of theory. To obtain true picture of the reaction path, we performed IRC calculations using CASSCF method with a minimal basis set 6-31G**. Some new equilibrium geometries and transition states have been identified at the CASSCF level. Energetics are also obtained at the QCISD(T)//CASSCF method. Possible reaction paths have been discussed, which are new in literature. Heat of reaction is found to be consistent with the experimental data. Bond dissociation energies to various dissociation paths are also reported.

Comparison of fleroxacin oxidation by chlorine and chlorine dioxide: Kinetics, mechanism and halogenated DBPs formation

Fleroxacin (FLE) is a widely used fluoroquinolones to cure urinary tract infections and respiratory disease, which has been frequently detected in the aquatic environment. The reactivity kinetics of FLE by chlorine and chlorine dioxide (ClO2) and transformation mechanism were investigated in this study. The results showed that FLE was degraded efficiently by chlorine and ClO2, and both reactions followed second-order kinetics overall. The increase of disinfectant dosage and temperature would enhance the degradation of FLE. The highest removal of FLE by chlorine was achieved at a neutral condition (pH 7.4), whereas ClO2 reaction rates increased dramatically with the increasing pH in this study condition. The number of intermediates identified in FLE chlorination and ClO2 oxidation was seven and ten, respectively. The piperazine ring cleavage was the principal and initial reaction in both above reactions. Then, the removal of the piperazine group was predominantly in FLE removal by chlorine, while the decarboxylation mainly occurred in FLE removal by ClO2. The intermediates increased first and then decreased with time, while three kinds of halogenated DBPs increased with time, indicating the above-identified intermediates were further transformed to the halogenated DBPs. Additionally, compared to chlorine reaction, the reaction of ClO2 with FLE reduced the formation of halogenated DBPs, but it also induced the formation of chlorite. The analysis of toxicity showed that compared with chlorination, the oxidation of ClO2 was more suitable for FLE removal.

Theoretical investigations on mechanisms and pathways of CH2FO2/CHF2O2 with ClO reactions in the atmosphere

The kinetics and mechanisms of the CH2FO2/CHF2O2 with ClO reactions have been investigated firstly by using the quantum chemical method. The single and triplet potential energy surfaces (PESs) of these two reactions have been obtained by using the BMC−CCSD method based on the geometries obtained at the B3LYP/6−311++G(d,p) level. For the CH2FO2 with ClO reaction, three activated intermediates, IM1 (CH2FOOOCl), IM2 (CH2FOOClO), and IM3 (CH2FOClO2) are generated along the reaction path, and then dissociate to various products. The similar production pathways are investigated for the CHF2O2 with ClO reaction. It should be noted that the isomerization of IM3 (CH2FOClO2) and the 1,3-Cl shift from IM1 (CH2FOOOCl) pathways were not found for the CH2FO2 with ClO reaction. The rate constants for the dominant product pathways are predicted by RRKM-TST theories. The major production pathway is the generation of IM1 (CH2FOOOCl)/IM1 (CHF2OOOCl) at 200−1200 K, and the generation of P1 (CHFO + HO2 +Cl)/P1 (CF2O + HO2 + Cl) by H-migration/elimination become dominant at higher temperatures for the CH2FO2/CHF2O2 + ClO reactions, respectively. The atmospheric lifetimes of CH2FO2 and CHF2O2 in ClO are around 11.38 and 8.65 h, respectively. Furthermore, on the basis of the analysis of the kinetics of all channels through which the addition and abstraction reactions proceed, we expect that the competitive power of reaction channels may vary with experimental conditions for the title reaction. The present study may be helpful for probing the mechanisms of the title reaction and understanding the halogen chemistry.

Atmospheric chemistry of CFCl2O2: a theoretical study on mechanisms and kinetics of the CFCl2O2 + ClO reaction.

The gas-phase reaction between CFCl2O2 and ClO was researched by means of quantum chemical methods. B3LYP method with the 6-311++G(d,p) basis set was used to obtain the geometric parameters of all stationary points including in the CFCl2O2 + ClO reaction. The singlet and triplet potential energy surfaces were characterized at the CCSD(T)/6-311++G(2d,2p)//B3LYP/6-311++G(d,p) level. Addition/elimination and SN2 displacement reaction mechanisms were identified on the singlet PES, and only substituent reaction mechanism was located on the triplet PES. The dominant reaction takes place on the singlet PES, and the major pathways are CFCl2O2 + ClO → IM1 (CFCl2OOOCl) → IM2 (CFCl2OOClO) → IM3 (CH3OClO2) → P6 (CFClO + (ClO)2). RRKM theory was used to calculate rate constants, which is consistent with the experimental data. The atmospheric lifetime of CFCl2O2 in ClO is around 8.84h. TD-DFT computations imply that IM1 (CFCl2OOOCl), IM2 (CFCl2OOClO), and IM3 (CFCl2OClO2) will photolyze under the sunlight. Graphical abstract.

Atmospheric chemistry of CHBr2O2: a theoretical study on mechanisms and kinetics of the CHBr2O2 + ClO reaction

CCSD(T)//B3LYP calculations of the potential energy surfaces (PESs) are associated with the rate constants and branch ratio of products using the RRKM (Rice–Ramsperger–Kassel–Marcus) theories to research the mechanism and product distribution of the CHBr2O2 with ClO reaction. The RRKM-computed theory reveals that IM1 (CHBr2OOOCl) are estimated to stable at T ≤ 500 K; the generating P1 (CBr2O + HO2 + Cl) was the primary product at T > 500 K. The lifetimes of CHBr2O2 in the presence of ClO are predicted to 27.8 h. Time-dependent density functional theory (TDDFT) calculations suggest that IM1 (CHBr2OOOCl), IM2 (CHBr2OOClO), and IM3 (CHBr2OClO2) will photolyze under the sunlight.

Ti/TiO2ntas/RuO2 Probe for Amperometric Detection of Hypochlorite in Solution

Tool to help provide a healthy environment. Disinfection is a process that is designed to kill actively growing and vegetative microbial microorganisms to a certain level. Generally, there are two methods of disinfection: chemical and physical1. The physical agents of disinfection that have been used include ultraviolet light (UV), electron beam, gamma-ray irradiation, sonication, and heat. Considering the chemical methods, there is a great variety of compounds such as chlorine, ozone, the metals copper and silver, phenolic compounds, quaternary ammonium salts, alcohols and hydrogen peroxide among others. Historically, the most widely used chemical disinfection procedure is chlorination because of its low cost, ease of application, and ability to inactivate a wide variety of pathogenic microorganisms.Hypochlorite ion (ClO-) is widely used in daily life applications such as household bleach, disinfection of drinking water and cooling-water treatment among others. Nevertheless, it has been reported that the abnormal production or the excessive intake of ClO- can lead to numerous diseases, including cardiovascular disorders, neuron degeneration, arthritis or even cancer2. Hence, it is of utmost importance to develop rapid and sensitive methods for the determination of ClO-. So far, iodometric titration and colorimetric methods based on the reaction of ClO- with organic reagents have been widely used so as to determine hypochlorite concentration. These methodologies usually require tedious procedures.In the present work, we propose the design of an amperometric sensor for fast hypochlorite analysis. The architecture of the sensor is a RuO2 coating onto a highly ordered titanium dioxide nanotube array (Ti/TiO2NTAs/RuO2). TiO2NTAs were grown by electrochemical anodization of a titanium metal disc in ethylene glycol containing ammonium fluoride (0.3%w/w) and water (2%w/w). The electrochemical synthesis was performed at 30V. Afterwards, RuO2 was deposited layer by layer onto the TiO2NTAs substrate and a final annealing process was performed at 500 oC in order to fix it to the nanostructure.The fundamental analytical parameters (linear range, limit of detection and sensitivity) of the probe were characterized in the presence of hypochlorite. The sensor working potential was also optimized and then fixed at 0.6 V. Finally, the hypochlorite content of different samples was measured using the sensor and compared with the DPD-method value (Standard Methods: 4500-Cl G)3. The proposed amperometric sensor offers an alternative tool to the classical DPD-method, with higher sensitivity, lower limit of quantification and analysis time.

Theoretical investigations on mechanisms and pathways of CH2ClO2/CHCl2O2 with ClO reactions in the atmosphere.

A global and systematic theoretical research on the singlet and triplet potential energy surfaces (PESs) of the CH2ClO2/CHCl2O2 with ClO reactions are done at the CCSD(T)//B3LYP level and accompanied with RRKM computations to forecast the mechanism and distribution of products. The simulation results revealed that, on the singlet PES, products P1 (CHClO + HO2 + Cl)/P1 (CCl2O + HO2 + Cl) from IM1 (CH2ClOOOCl)/IM1 (CHCl2OOOCl) are forecasted to the primary products of the CH2ClO2/CHCl2O2 + ClO reactions, which are initiated by the oxygen atom of ClO radical addition to the terminal-O atom of CH2ClO2/CHCl2O2 barrierlessly, while other product channels contribute less to the whole reactions owing to higher barriers. Two other isomers, including IM2 (CH2ClOOClO) and IM3 (CH2ClOClO2) for the CH2ClO2 + ClO reaction, and three other isomers, including IM2 (CHCl2OOClO), IM3 (CHCl2OClO2), and IM4 (CHCl2ClO3) for the CHCl2O2 + ClO reaction, could be produced as less significant products. RRKM calculations presented that the initial adducts IM1 (CH2ClOOOCl)/IM1 (CHCl2OOOCl) are the primary products at T < 400K and T < 600K, respectively, and products P1 (CHClO + HO2 + Cl)/P1 (CCl2O + HO2 + Cl) are dominant the reactions at T ≥ 400K and T ≥ 600K, respectively. The atmospheric lifetime of CH2ClO2 and CHCl2O2 in ClO is around 4.61 and 3.24h, respectively.

Chlorine partitioning near the polar vortex edge observed with ground-based FTIR and satellites at Syowa Station, Antarctica, in 2007 and 2011

Abstract. We retrieved lower stratospheric vertical profiles of O3, HNO3, and HCl from solar spectra taken with a ground-based Fourier transform infrared spectrometer (FTIR) installed at Syowa Station, Antarctica (69.0∘ S, 39.6∘ E), from March to December 2007 and September to November 2011. This was the first continuous measurement of chlorine species throughout the ozone hole period from the ground in Antarctica. We analyzed temporal variation of these species combined with ClO, HCl, and HNO3 data taken with the Aura MLS (Microwave Limb Sounder) satellite sensor and ClONO2 data taken with the Envisat MIPAS (the Michelson Interferometer for Passive Atmospheric Sounding) satellite sensor at 18 and 22 km over Syowa Station. An HCl and ClONO2 decrease occurred from the end of May at both 18 and 22 km, and eventually, in early winter, both HCl and ClONO2 were almost depleted. When the sun returned to Antarctica in spring, enhancement of ClO and gradual O3 destruction were observed. During the ClO-enhanced period, a negative correlation between ClO and ClONO2 was observed in the time series of the data at Syowa Station. This negative correlation was associated with the relative distance between Syowa Station and the edge of the polar vortex. We used MIROC3.2 chemistry–climate model (CCM) results to investigate the behavior of whole chlorine and related species inside the polar vortex and the boundary region in more detail. From CCM model results, the rapid conversion of chlorine reservoir species (HCl and ClONO2) into Cl2, gradual conversion of Cl2 into Cl2O2, increase in HOCl in the winter period, increase in ClO when sunlight became available, and conversion of ClO into HCl were successfully reproduced. The HCl decrease in the winter polar vortex core continued to occur due to both transport of ClONO2 from the subpolar region to higher latitudes, providing a flux of ClONO2 from more sunlit latitudes into the polar vortex, and the heterogeneous reaction of HCl with HOCl. The temporal variation of chlorine species over Syowa Station was affected by both heterogeneous chemistries related to polar stratospheric cloud (PSC) occurrence inside the polar vortex and transport of a NOx-rich air mass from the polar vortex boundary region, which can produce additional ClONO2 by reaction of ClO with NO2. The deactivation pathways from active chlorine into reservoir species (HCl and/or ClONO2) were confirmed to be highly dependent on the availability of ambient O3. At 18 km, where most ozone was depleted, most ClO was converted to HCl. At 22 km where some O3 was available, an additional increase in ClONO2 from the prewinter value occurred, similar to the Arctic.

Computational study on the mechanisms and kinetics of the CH2BrO2 + ClO reaction in the atmosphere.

The singlet and triplet potential energy surfaces for the CH2BrO2 + ClO reaction are studied at the CCSD(T)/cc-pVTZ//B3LYP/6-311++G(d,p) level. CH2BrO2 is revealed to react with ClO through two kinds of mechanisms on the triplet potential energy surface (PES), namely, SN2 displacement and H-abstraction, and the production of P3 (CHBrO2 + HOCl) via H-abstraction is the dominant channel. Addition/elimination and SN2 displacement mechanisms exist on the singlet PES and are more complicated. The RRKM calculations of the mechanism and product distribution in the CH2BrO2 + ClO reaction show that the stabilization of IM1 (CH2BrOOOBr) is dominant at T ≤ 600 K, while the pathway of producing P1 (CHBrO + HO2 + Cl) occupies the entire reaction at T > 600 K. The total rate constants are independent of pressure, while the individual rate constants are sensitive to pressure. The lifetime of CH2BrO2 in the presence of ClO is estimated to be 20.27 h. Moreover, time-dependent density functional theory (TDDFT) calculations suggest that IM1 (CH2BrOOOCl), IM2 (CH2BrOOClO) and IM3 (CH2BrOClO2) will photolyze under the sunlight.

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.

Springtime Nitrogen Oxide-Influenced Chlorine Chemistry in the Coastal Arctic.

Atomic chlorine (Cl) is a strong atmospheric oxidant that shortens the lifetimes of pollutants and methane in the springtime Arctic, where the molecular halogens Cl2 and BrCl are known Cl precursors. Here, we quantify the contributions of reactive chlorine trace gases and present the first observations, to our knowledge, of ClNO2 (another Cl precursor), N2O5, and HO2NO2 in the Arctic. During March - May 2016 near Utqiaġvik, Alaska, up to 21 ppt of ClNO2, 154 ppt of Cl2, 27 ppt of ClO, 71 ppt of N2O5, 21 ppt of BrCl, and 153 ppt of HO2NO2 were measured using chemical ionization mass spectrometry. The main Cl precursor was calculated to be Cl2 (up to 73%) in March, while BrCl was a greater contributor (63%) in May, when total Cl production was lower. Elevated levels of ClNO2, N2O5, Cl2, and HO2NO2 coincided with pollution influence from the nearby town of Utqiaġvik and the North Slope of Alaska (Prudhoe Bay) Oilfields. We propose a coupled mechanism linking NOx with Arctic chlorine chemistry. Enhanced Cl2 was likely the result of the multiphase reaction of Cl-(aq) with ClONO2, formed from the reaction of ClO and NO2. In addition to this NOx-enhanced chlorine chemistry, Cl2 and BrCl were observed under clean Arctic conditions from snowpack photochemical production. These connections between NOx and chlorine chemistry, and the role of snowpack recycling, are important given increasing shipping and fossil fuel extraction predicted to accompany Arctic sea ice loss.

Chlorine nitrate in the atmosphere

Abstract. This review article compiles the characteristics of the gas chlorine nitrate and discusses its role in atmospheric chemistry. Chlorine nitrate is a reservoir of both stratospheric chlorine and nitrogen. It is formed by a termolecular reaction of ClO and NO2. Sink processes include gas-phase chemistry, photo-dissociation, and heterogeneous chemistry on aerosols. The latter sink is particularly important in the context of polar spring stratospheric chlorine activation. ClONO2 has vibrational–rotational bands in the infrared, notably at 779, 809, 1293, and 1735 cm−1, which are used for remote sensing of ClONO2 in the atmosphere. Mid-infrared emission and absorption spectroscopy have long been the only concepts for atmospheric ClONO2 measurements. More recently, fluorescence and mass spectroscopic in situ techniques have been developed. Global ClONO2 distributions have a maximum at polar winter latitudes at about 20–30 km altitude, where mixing ratios can exceed 2 ppbv. The annual cycle is most pronounced in the polar stratosphere, where ClONO2 concentrations are an indicator of chlorine activation and de-activation.

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.

Theoretical investigations on the atmospheric C 2 H 5 O 2 + ClO reaction

Abstract Mechanisms and channels of the C2H5O2 + ClO reaction in atmosphere were investigated using quantum chemistry method, i.e., CCSD(T)/6-311++G(2d,2p)//B3LYP/6-311++G(d,p) levels of theory. Our result indicates that the title reaction occurs on both the singlet and triplet potential energy surfaces (PESs). Kinetically, C2H5O3Cl and C2H5O + ClOO on the singlet PES were dominant in atmosphere; while other products including CH3CHO2 + HOCl, CH3CHO + HOClO, and CH3CHO + HClO2 make minor contributions to overall reaction due to high barriers and unstable formations. Moreover, time-dependent density functional theory (TDDFT) calculation on the vertical excitation energy implies that C2H5O3Cl will photolyze under the sunlight.

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.

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.