Temperature‐Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates

The rate coefficients for gas‐phase reaction of trifluoroacetic acid (TFA) with two Criegee intermediates, formaldehyde oxide and acetone oxide, decrease with increasing temperature in the range 240–340 K. The rate coefficients k(CH₂OO + CF₃COOH)=(3.4±0.3)×10⁻¹⁰ cm³ s⁻¹ and k((CH₃)₂COO + CF₃COOH)=(6.1±0.2)×10⁻¹⁰ cm³ s⁻¹ at 294 K exceed estimates for collision‐limited values, suggesting rate enhancement by capture mechanisms because of the large permanent dipole moments of the two reactants. The observed temperature dependence is attributed to competitive stabilization of a pre‐reactive complex. Fits to a model incorporating this complex formation give k [cm³ s⁻¹]=(3.8±2.6)×10⁻¹⁸ T² exp((1620±180)/T) + 2.5×10⁻¹⁰ and k [cm³ s⁻¹]=(4.9±4.1)×10⁻¹⁸ T² exp((1620±230)/T) + 5.2×10⁻¹⁰ for the CH₂OO + CF₃COOH and (CH₃)₂COO + CF₃COOH reactions, respectively. The consequences are explored for removal of TFA from the atmosphere by reaction with biogenic Criegee intermediates.     

Heteroatom Tuning of Bimolecular Criegee Reactions and Its Implications

High‐level quantum‐chemical calculations have been performed to understand the key reactivity determinants of bimolecular reactions of Criegee intermediates and H₂X (X=O, S, Se, and Te). Criegee intermediates are implicated as key intermediates in atmospheric, synthetic organic, and enzymatic chemistry. Generally, it is believed that the nature and location of substituents at the carbon of the Criegee intermediate play a key role in determing the reactivity. However, the present work suggests that it is not only the substitution of the Criegee intermediate, but the nature of the heteroatom in H₂X that also plays a crucial role in determining the reactivity of the interaction between the Criegee intermediate and H₂X. The barriers for the reactions of Criegee intermediates and H₂X satisfy an inverse correlation with the bond strength of X−H in H₂X, and a direct correlation with the first pK_a of H₂X. This heteroatom tuning causes a substantial barrier lowering of 8–11 kcal mol⁻¹ in the Criegee reaction barrier in going from H₂O to H₂Te. An important implication of these results is that the reaction of the Criegee intermediate and H₂S could be a source of thioaldehydes, which are important in plantery atmospheres and synthetic organic chemistry. By performing the reaction of Criegee intermediates and H₂S under water or acid catalysis, thioladehydes could be detected in a hydrogen‐bonded complexed state, which is significantly more stable than their uncomplexed form. As a result, simpler aliphatic thioaldehydes could be selectively synthesized in the laboratory, which, otherwise, has been a significant synthetic challenge because of their ability to oligomerize.     

Temperature-dependent kinetics of the simplest Criegee intermediate reaction with dimethyl sulfoxide

Criegee intermediates are thought to play roles in atmospheric chemistry, including OH radical formation, oxidation of SO₂, NO₂, etc. CH₂OO is the simplest Criegee intermediate, of which the reactivity has been a hot topic. Here we investigated the kinetics of CH₂OO reaction with dimethyl sulfoxide (DMSO) under 278–349 K and 10–150 Torr. DMSO is an important species formed in the oxidation of dimethyl sulfide in the biogenic sulfur cycle. The concentration of CH₂OO was monitored in real-time via its mid-infrared absorption band at about 1,286 cm⁻¹ (Q branch of the ν₄ band) with a high-resolution quantum cascade laser spectrometer. The 298 K bimolecular rate coefficient was determined to be k₂₉₈ = (2.3 ± 0.3) × 10⁻¹² cm³/s at 30 Torr with an Arrhenius activation energy of −3.9 ± 0.2 kcal/mol and a weak pressure dependence for pressures higher than 30 Torr (k₂₉₈ = (2.8 ± 0.3) × 10⁻¹² cm³/s at 100 Torr). The reaction is speculated to undergo a five-membered ring intermediate, analogous to that of CH₂OO with SO₂. The negative activation energy indicates that the rate-determining transition state is submerged. The magnitude of the reaction rate coefficient lies in between those of CH₂OO reactions with (CH₃)₂CO and with SO₂.     

Rate Coefficients of C1 and C2 Criegee Intermediate Reactions with Formic and Acetic Acid Near the Collision Limit: Direct Kinetics Measurements and Atmospheric Implications

Rate coefficients are directly determined for the reactions of the Criegee intermediates (CI) CH₂OO and CH₃CHOO with the two simplest carboxylic acids, formic acid (HCOOH) and acetic acid (CH₃COOH), employing two complementary techniques: multiplexed photoionization mass spectrometry and cavity‐enhanced broadband ultraviolet absorption spectroscopy. The measured rate coefficients are in excess of 1×10^?10 cm³ s^?1, several orders of magnitude larger than those suggested from many previous alkene ozonolysis experiments and assumed in atmospheric modeling studies. These results suggest that the reaction with carboxylic acids is a substantially more important loss process for CIs than is presently assumed. Implementing these rate coefficients in global atmospheric models shows that reactions between CI and organic acids make a substantial contribution to removal of these acids in terrestrial equatorial areas and in other regions where high CI concentrations occur such as high northern latitudes, and implies that sources of acids in these areas are larger than previously recognized.     

Electronic Absorption Spectroscopy and Photochemistry of Criegee Intermediates

Interest in Criegee intermediates (CIs), often termed carbonyl oxides, and their role in tropospheric chemistry has grown massively since the demonstration of laboratory-based routes to their formation and characterization in the gas phase. This article reviews current knowledge regarding the electronic spectroscopy of atmospherically relevant CIs like CH₂OO, CH₃CHOO, (CH₃)₂COO and larger CIs like methyl vinyl ketone oxide and methacrolein oxide that are formed in the ozonolysis of isoprene, and of selected conjugated carbene-derived CIs of interest in the synthetic chemistry community. Of the aforementioned atmospherically relevant CIs, all except CH₂OO and (CH₃)₂COO exist in different conformers which, under tropospheric conditions, can display strikingly different thermal loss rates via unimolecular and bimolecular processes. Calculated photolysis rates based on their absorption properties suggest that solar photolysis will rarely be a significant contributor to the total loss rate for any CI under tropospheric conditions. Nonetheless, there is ever-growing interest in the absorption cross sections and primary photochemistry of CIs following excitation to the strongly absorbing ¹ππ* state, and how this varies with CI, with conformer and with excitation wavelength. The later part of this review surveys the photochemical data reported to date, including a range of studies that demonstrate prompt photo-induced fission of the terminal O–O bond, and speculates about possible alternate decay processes that could occur following non-adiabatic coupling to, and dissociation from, highly internally excited levels of the electronic ground state of a CI.     

反式2-甲基-2-丁烯酸甲酯与臭氧反应机理的计算研究

采用G3B3方法构建反式2-甲基-2-丁烯酸甲酯与O3反应体系以及后续Criegee自由基有、无水分子参与下异构化反应的势能面剖面.结果表明,反式2-甲基-2-丁烯酸甲酯与O3反应首先生成一个稳定的五元环中间体,此中间体按断键位置不同后续裂解反应存在两条路径,分别生成产物P1(CH3CHOO+CH3OC(O)C(CH3)O)和P2(CH3CHO+CH3OC(O)C(CH3)OO).利用经典过渡态理论(TST)并结合Wigner矫正模型计算了200-1200 K温度区间内标题反应的速率常数kTST/W.计算结果显示,294 K时,该反应速率常数为7.55×10-18cm3molecule-1s-1,与Bernard等对类似反应所测实验值非常接近.生成的Criegee自由基(CH3CHOO和CH3OC(O)C(CH3)OO)可分别与水分子发生α-加成及β-氢迁移反应,其中Criegee自由基与水的α-加成反应较其与水的β-氢迁移反应具有优势.另外与无水分子参与CH3CHOO和CH3OC(O)C(CH3)OO异构化反应相比,水分子的参与使得异构化反应较为容易进行.     

High reactivity of hexafluoro acetone toward criegee intermediates in the gas‐phase ozonolysis of simple alkenes

Hexafluoro acetone CF₃COCF₃ has been shown to react rapidly with the CH₂OO, CH₃CHOO, and (CH₃)₂COO intermediates that are formed in the ozonolysis of C₂H₄, trans‐2‐C₄H₈, and 2,3‐dimethyl‐2‐butene, respectively, and to form products tentatively assigned to the corresponding secondary ozonides. Relative rate method applied to the C₂H₄ ozonolysis has indicated that CF₃COCF₃ reacts ∼13 times faster than CH₃CHO. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 261–269, 1999     

Isomerization and Decomposition of a Criegee Intermediate in the Ozonolysis of Alkenes: Dynamics Using a Multireference Potential

The isomerization and decomposition dynamics of the simplest Criegee intermediate CH₂OO have been studied by classical trajectory simulations using the multireference ab initio MR‐PT2 potential on the fly. A new, accelerated algorithm for dynamics with MR‐PT2 was used. For an initial temperature of 300 K, starting from the transition state from CH₂OO→CH₂O₂ , the system reaches the dioxirane structure in around 50 fs, then isomerizes to formic acid (in ca. 2800 fs), and decomposes into CO+H₂O at around 2900 fs. The contributions of different configurations to the multiconfigurational total electronic wave function vary dramatically along the trajectory, with diradical contributions being important for transition states corresponding to H‐atom transfers, while being only moderately significant for CH₂OO. The implications for reactions of Criegee intermediates are discussed.     

Spectroscopy of the Simplest Criegee Intermediate CH2OO: Simulation of the First Bands in Its Electronic and Photoelectron Spectra

CH₂OO, the simplest Criegee intermediate, and ozone are isoelectronic. They both play very important roles in atmospheric chemistry. Whilst extensive experimental studies have been made on ozone, there were no direct gas‐phase studies on CH₂OO until very recently when its photoionization spectrum was recorded and kinetics studies were made of some reactions of CH₂OO with a number of molecules of atmospheric importance, using photoionization mass spectrometry to monitor CH₂OO. In order to encourage more direct studies on CH₂OO and other Criegee intermediates, the electronic and photoelectron spectra of CH₂OO have been simulated using high level electronic structure calculations and Franck–Condon factor calculations, and the results are presented here. Adiabatic and vertical excitation energies of CH₂OO were calculated with TDDFT, EOM‐CCSD, and CASSCF methods. Also, DFT, QCISD and CASSCF calculations were performed on neutral and low‐lying ionic states, with single energy calculations being carried out at higher levels to obtain more reliable ionization energies. The results show that the most intense band in the electronic spectrum of CH₂OO corresponds to the ${{\rm{\tilde B}}}$ ¹A′ ← ${{\rm{\tilde X}}}$ ¹A′ absorption. It is a broad band in the region 250–450 nm showing extensive structure in vibrational modes involving O–O stretching and C‐O‐O bending. Evidence is presented to show that the electronic absorption spectrum of CH₂OO has probably been recorded in earlier work, albeit at low resolution. We suggest that CH₂OO was prepared in this earlier work from the reaction of CH₂I with O₂ and that the assignment of the observed spectrum solely to CH₂IOO is incorrect. The low ionization energy region of the photoelectron spectrum of CH₂OO consists of two overlapping vibrationally structured bands corresponding to one‐electron ionizations from the highest two occupied molecular orbitals of the neutral molecule. In each case, the adiabatic component is the most intense and the adiabatic ionization energies of these bands are expected to be very close, at 9.971 and 9.974 eV at the highest level of theory used.     

Theoretical study of reaction channels for the weakly bound complex systems created with HF,CO2, and various amines

This investigation conducted reaction channels of weakly bound complexes CO₂…HF, CO₂…HF…NH₃, CO₂…HF…NH₂CH₃, CO₂…HF…NH(CH₃)₂, and CO₂…HF…N(CH₃)₃ systems, using the Gaussian 98 package at the B3LYP/6‐311++G(3df,2pd) level. The syn‐fluoroformic acid or syn‐fluoroformic acid plus NH₃ or amine conformers are more stable than the related anti‐fluoroformic acid or anti‐fluoroformic acid plus NH₃ or amine conformers. However, the above‐mentioned weakly bound complexes are more stable than both the related syn‐ and anti‐type fluoroformic acid or acid plus NH₃ or amine conformers and their related decomposed into CO₂ + HF or CO₂ + NHR₃F (R?H, CH₃) combined molecular systems. Five reaction channels of the weakly bound complexes exist. Each channel includes weakly bound complexes and their related above‐mentioned systems. Moreover, each reaction channel contains two transition states. The transition state between the weakly bound complex and anti‐fluoroformic acid type structure (T₁₃) is significantly higher than that of internal rotation (T₂₃) between syn‐ and anti‐FCO₂H (or FCO₂H…NR₃) structures. However, the above‐mentioned T₁₃ can significantly decrease its energy by adding the third molecule NH₃ or NR₃ (R?H or CH₃). The more CH₃ that is substituted in NR₃ of the reaction channel, the lower the activation energy of the transition state in the system is affected. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

An Estimation of the Levels of Stabilized Criegee Intermediates in the UK Urban and Rural Atmosphere Using the Steady‐State Approximation and the Potential Effects of These Intermediates on Tropospheric Oxidation Cycles

Levels of the stabilized Criegee Intermediate (sCI), produced via the ozonolysis of unsaturated volatile organic compounds (VOCs), were estimated at two London urban sites (Marylebone Road and Eltham) and one rural site (Harwell) in the UK over the period of 1998–2012. The steady‐state approximation was applied to data obtained from the NETCEN (National Environmental Technology Centre) database, and the levels of annual average sCI were estimated to be in the range of 30–3000 molecules cm⁻³ for UK sites. A consistent diurnal cycle of sCI concentration is estimated for the UK sites with increasing levels during daylight hours, peaking just after midday. The seasonal pattern of sCI shows higher levels in spring with peaks around May due to the higher levels of O₃. The ozone weekend effect resulted in higher sCI in UK urban areas during weekend. The sCI data were modeled using the information provided by the Air Quality Improvement Research Program (AQIRP) and found that the modeled production was five‐ to six‐fold higher than our estimated data, and therefore the estimated sCI concentrations in this study are thought to be lower estimates only. Compared with nighttime, 1.3‐ to 1.8‐fold higher sCI exists under daytime conditions. Using the levels of sCI estimated at Marylebone Road, globally the oxidation rates of NO₂ + sCI (22.4 Gg/yr) and SO₂ + sCI (37.6 Gg/yr) in urban areas can increase their effect in the troposphere and potentially further alter the oxidizing capacity of the troposphere. Further investigations of modeled sCI show that CH₃CHOO (64%) and CH₂OO (13%) are dominant among all contributing sCI at the UK sites.     

CO2 Hydrogenation on Cu/Al2O3: Role of the Metal/Support Interface in Driving Activity and Selectivity of a Bifunctional Catalyst

Selective hydrogenation of CO₂ into methanol is a key sustainable technology, where Cu/Al₂O₃ prepared by surface organometallic chemistry displays high activity towards CO₂ hydrogenation compared to Cu/SiO₂, yielding CH₃OH, dimethyl ether (DME), and CO. CH₃OH formation rate increases due to the metal–oxide interface and involves formate intermediates according to advanced spectroscopy and DFT calculations. Al₂O₃ promotes the subsequent conversion of CH₃OH to DME, showing bifunctional catalysis, but also increases the rate of CO formation. The latter takes place 1) directly by activation of CO₂ at the metal–oxide interface, and 2) indirectly by the conversion of formate surface species and CH₃OH to methyl formate, which is further decomposed into CH₃OH and CO. This study shows how Al₂O₃, a Lewis acidic and non‐reducible support, can promote CO₂ hydrogenation by enabling multiple competitive reaction pathways on the oxide and metal–oxide interface.     

Gas‐Phase Structure Determination of Dihydroxycarbene,One of the Smallest Stable Singlet Carbenes

Carbenes are reactive molecules of the form R¹ C̈ R² that play a role in topics ranging from organic synthesis to gas‐phase oxidation chemistry. We report the first experimental structure determination of dihydroxycarbene (HO C̈ OH), one of the smallest stable singlet carbenes, using a combination of microwave rotational spectroscopy and high‐level coupled‐cluster calculations. The semi‐experimental equilibrium structure derived from five isotopic variants of HO C̈ OH contains two very short CO single bonds (ca. 1.32 Å). Detection of HO C̈ OH in the gas phase firmly establishes that it is stable to isomerization, yet it has been underrepresented in discussions of the CH₂O₂ chemical system and its atmospherically relevant isomers: formic acid and the Criegee intermediate CH₂OO.     

UV Spectrum of the Simplest Deuterated Criegee Intermediate CD2OO

The ultraviolet (UV ) absorption spectrum of the simplest deuterated Criegee intermediate CD₂OO has been measured and compared with that of CH₂OO . While the UV spectra of CH₂OO and CD₂OO are similar in the overall shape, distinctive oscillatory structures at the long wavelength side of the absorption band show clear effect of isotopic substitution. The average spacing between the vibrational peaks decreases from 606 cm⁻¹ for CH₂OO to 528 cm⁻¹ for CD₂OO . This large isotope effect cannot be explained by one‐dimensional model along the dissociative O−O bond. Instead, vibrational modes involving motions of the H‐atoms are expected to be responsible for the observed oscillatory structure. This isotope effect offers a stringent test for theoretical investigations on the absorption spectrum and excited‐state dynamics of the simplest Criegee intermediate.     

Theoretical Study of the Reaction of Carbonyl Oxide with Nitrogen Dioxide: CH2OO + NO2

The reaction mechanism of the reaction of the Criegee intermediate CH₂OO with NO₂ was investigated using quantum chemical and theoretical kinetic methodologies. The reaction shows a rich chemistry, though the number of channels that effectively contribute at room temperature is limited. The theoretical characterization of the entrance transition states was hampered by strongly multireference wave functions. The predicted rate coefficient k (298 K) = 4.4 × 10⁻¹² cm³ molecule⁻¹ s⁻¹ thus carries a large uncertainty, but is in agreement with literature data. We find that the CH₂OO + NO₂ reaction reacts by adduct formation, near‐exclusively forming nitro‐peroxy radicals, ^•OOCH₂NO₂. These will react as other alkylperoxy radicals in the atmosphere, ultimately generating CH₂O and regenerating NO₂ in most reaction conditions. The product predictions contrast with earlier experimental work showing NO₃ formation, but support other observations of adduct products.     

Temperature-Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates

The rate coefficients for gas-phase reaction of trifluoroacetic acid (TFA) with two Criegee intermediates, formaldehyde oxide and acetone oxide, decrease with increasing temperature in the range 240–340 K. The rate coefficients k(CH₂OO + CF₃COOH)=(3.4±0.3)×10⁻¹⁰ cm³ s⁻¹ and k((CH₃)₂COO + CF₃COOH)=(6.1±0.2)×10⁻¹⁰ cm³ s⁻¹ at 294 K exceed estimates for collision-limited values, suggesting rate enhancement by capture mechanisms because of the large permanent dipole moments of the two reactants. The observed temperature dependence is attributed to competitive stabilization of a pre-reactive complex. Fits to a model incorporating this complex formation give k [cm³ s⁻¹]=(3.8±2.6)×10⁻¹⁸ T² exp((1620±180)/T) + 2.5×10⁻¹⁰ and k [cm³ s⁻¹]=(4.9±4.1)×10⁻¹⁸ T² exp((1620±230)/T) + 5.2×10⁻¹⁰ for the CH₂OO + CF₃COOH and (CH₃)₂COO + CF₃COOH reactions, respectively. The consequences are explored for removal of TFA from the atmosphere by reaction with biogenic Criegee intermediates.     

Temperature‐ and Pressure‐Dependent Kinetics of CH2OO + CH3COCH3 and CH2OO + CH3CHO: Direct Measurements and Theoretical Analysis

The rate coefficients of the gas‐phase reactions CH₂OO + CH₃COCH₃ and CH₂OO + CH₃CHO have been experimentally determined from 298–500 K and 4–50 Torr using pulsed laser photolysis with multiple‐pass UV absorption at 375 nm, and products were detected using photoionization mass spectrometry at 10.5 eV. The CH₂OO + CH₃CHO reaction's rate coefficient is ～4 times faster over the temperature 298–500 K range studied here. Both reactions have negative temperature dependence. The T dependence of both reactions was captured in simple Arrhenius expressions: The rate of the reactions of CH₂OO with carbonyl compounds at room temperature is two orders of magnitude higher than that reported previously for the reaction with alkenes, but the A factors are of the same order of magnitude. Theoretical analysis of the entrance channel reveals that the inner 1,3‐cycloaddition transition state is rate limiting at normal temperatures. Predicted rate‐coefficients (RCCSD(T)‐F12a/cc‐pVTZ‐F12//B3LYP/MG3S level of theory) in the low‐pressure limit accurately reproduce the experimentally observed temperature dependence. The calculations only qualitatively reproduce the A factors and the relative reactivity between CH₃CHO and CH₃COCH₃. The rate coefficients are weakly pressure dependent, within the uncertainties of the current measurements. The predicted major products are not detectable with our photoionization source, but heavier species yielding ions with masses m/z = 104 and 89 are observed as products from the reaction of CH₂OO with CH₃COCH₃. The yield of m/z = 89 exhibits positive pressure dependence that appears to have already reached a high‐pressure limit by 25 Torr.     

Reactions of stabilized criegee intermediates from the gas‐phase reactions of O3 with selected alkenes

The gas‐phase reactions of O₃ with 1‐octene, trans‐7‐tetradecene, 1,2‐dimethyl‐1‐cyclohexene, and α‐pinene have been studied in the presence of an OH radical scavenger, primarily using in situ atmospheric pressure ionization tandem mass spectrometry (API‐MS), to investigate the products formed from the reactions of the thermalized Criegee intermediates in the presence of water vapor and 2‐butanol (1‐octene and trans‐7‐tetradecene forming the same Criegee intermediate). With H₃O⁺(H₂O)_n as the reagent ions, ion peaks at 149 u ([M + H]⁺) were observed in the API‐MS analyses of the 1‐octene and trans‐7‐tetradecene reactions, which show a neutral loss of 34 u (H₂O₂) and are attributed to the α‐hydroxyhydroperoxide CH₃(CH₂)₅CH(OH)OOH, which must therefore have a lifetime with respect to decomposition of tens of minutes or more. No evidence for the presence of α‐hydroxyhydroperoxides was obtained in the 1,2‐dimethyl‐1‐cyclohexene or α‐pinene reactions, although the smaller yields of thermalized Criegee intermediates in these reactions makes observation of α‐hydroxyhydroperoxides from these reactions less likely than from the 1‐octene and trans‐7‐tetradecene reactions. Quantifications of 2,7‐octanedione from the 1,2‐dimethyl‐1‐cyclohexene reactions and of pinonaldehyde from the α‐pinene reactions were made by gas chromatographic analyses during reactions with cyclohexane and with 2‐butanol as the OH radical scavenger. The measured yields of 2,7‐octanedione from 1,2‐dimethyl‐1‐cyclohexene and of pinonaldehyde from α‐pinene were 0.110 ± 0.020 and 0.164 ± 0.029, respectively, and were independent of the OH radical scavenger used. Reaction mechanisms are presented and discussed. © 2001 Wiley Periodicals, Inc. Int J Chem Kinet 34: 73–85, 2002     

The reactions of the Criegee intermediate CH3 CHOO in the gas-phase ozonolysis of 2-butene isomers

Ozonolysis of cis- and trans-2-butene isomers were carried out in a 570 l spherical glass vessel in 730 torr synthetic air at 295 ± 3 K. The initial concentrations were 5 to 10 ppmv for the isomers and 2 to 5 ppmv for ozone. Quantitative yields were determined by FTIR spectroscopy for CH₃CHO, HCHO, CH₄, CH₃OH, CO, and CO₂. By means of computational subtraction of the spectral contribution of the identified products from the product spectra, residual spectra have been obtained. Formation of 2-butene ozonide, propene ozonide, and l-hydroperoxyethyl formate CH₃CH(OOH)(SINGLE BOND)O(SINGLE BOND)CH(O) have been identified in the residual spectra. These products have been shown to be formed in the reactions of the Criegee intermediate CH₃CHOO with CH₃CHO, HCHO, and HCOOH, respectively. Mechanistic implications and atmospheric relevance of these observations are discussed. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 461–468, 1997.     

Mechanistic Insight into the Reaction of Organic Acids with SO3 at the Air–Water Interface

The gas‐phase reaction of organic acids with SO₃ has been recognized as essential in promoting aerosol‐particle formation. However, at the air–water interface, this reaction is much less understood. We performed systematic Born–Oppenheimer molecular dynamics (BOMD) simulations to study the reaction of various organic acids with SO₃ on a water droplet. The results show that with the involvement of interfacial water molecules, organic acids can react with SO₃ and form the ion pair of sulfuric‐carboxylic anhydride and hydronium. This mechanism is in contrast to the gas‐phase reaction mechanisms in which the organic acid either serves as a catalyst for the reaction between SO₃ and H₂O or reacts with SO₃ directly. The distinct reaction at the water surface has important atmospheric implications, for example, promoting water condensation, uptaking atmospheric condesation species, and incorporating “SO₄^2?” into organic species in aerosol particles. Therefore, this reaction, typically occurring within a few picoseconds, provides another pathway towards aerosol formation.