The HO 4 H → O 3 + H 2 O reaction catalysed by acidic, neutral and basic catalysts in the troposphere

Long

Mitchell

et al. 2021

ACS Earth Space Chem.

Self Cite

Formaldehyde (HCHO) plays an important role in the formation of secondary organic aerosols. Here, we report new mechanistic pathways for the reactions of formaldehyde with formic acid catalyzed by sulfuric acid and formaldehyde with sulfuric acid catalyzed by formic acid by using quantum chemical methods and reaction rate theory. We have found that sulfuric acid and formic acid have a strong catalytic role in the HCHO••• HCOOH + H 2 SO 4 and HCHO•••H 2 SO 4 + HCOOH reactions because the calculated energy barriers of the sulfuric acid-catalyzed reaction of formaldehyde with formic acid and formic acid-catalyzed reaction of formaldehyde with sulfuric acid are decreased by 21.17 and 14.81 kcal/mol, respectively. The calculated rates show that the reaction rate of HCHO••• HCOOH + H 2 SO 4 is faster than those of HCHO•••H 2 SO 4 + HCOOH and HCHO + HCOOH•••H 2 SO 4 . Moreover, the HCHO + HCOOH + H 2 SO 4 → H 2 C(OH)OCOH + H 2 SO 4 reaction readily forms the carboxylic acid ester (H 2 C(OH)OCOH); this is a new mechanistic pathway for the reaction of formaldehyde with formic acid, which is expected to extend to other aldehydes' reaction with carboxylic acids. Additionally, the present findings also suggest that formic acid-catalyzed formaldehyde and sulfuric acid reaction leads to the formation of an organosulfate as the nucleation precursor. The present results not only help understand the mechanisms for the initial processes of atmospheric nucleation but also are expected to extend other aldehydes and acids in the atmosphere.

Section: Introductionmentioning

confidence: 99%

New Mechanistic Pathways for the Reactions of Formaldehyde with Formic Acid Catalyzed by Sulfuric Acid and Formaldehyde with Sulfuric Acid Catalyzed by Formic Acid: Formation of Potential Secondary Organic Aerosol Precursors

Long

Mitchell

et al. 2021

ACS Earth Space Chem.

Self Cite

“…Ample theoretical and experimental investigations have been carried out for to investigate its mechanisms and kinetics over a wide range of temperatures and pressures. ,,− Interestingly, it has been found that the rate coefficients of , denoted hereafter as k 1 (in the units of cm 3 molecule –1 s –1 if not specified otherwise), show a minimum around 700–800 K. Further, the effect of pressure on k 1 is significant at low temperatures but vanishes at temperatures above 600 K.…”

mentioning

confidence: 99%

Permutation-Invariant-Polynomial Neural-Network-Based Δ-Machine Learning Approach: A Case for the HO₂ Self-Reaction and Its Dynamics Study

2022

J. Phys. Chem. Lett.

Δ-machine learning, or the hierarchical construction scheme, is a highly cost-effective method, as only a small number of high-level ab initio energies are required to improve a potential energy surface (PES) fit to a large number of low-level points. However, there is no efficient and systematic way to select as few points as possible from the low-level data set. We here propose a permutation-invariant-polynomial neural-network (PIP-NN)-based Δ-machine learning approach to construct full-dimensional accurate PESs of complicated reactions efficiently. Particularly, the high flexibility of the NN is exploited to efficiently sample points from the low-level data set. This approach is applied to the challenging case of a HO2 self-reaction with a large configuration space. Only 14% of the DFT data set is used to successfully bring a newly fitted DFT PES to the UCCSD(T)-F12a/AVTZ quality. Then, the quasiclassical trajectory (QCT) calculations are performed to study its dynamics, particularly the mode specificity.

Section: Toc Graphics Abstractmentioning

confidence: 99%

“…10 Ample theoretical and experimental investigations have been carried out for R1 to investigate its mechanisms and kinetics over a wide range of temperatures and pressures. 4,6,[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Interestingly, it has been found that the rate coefficients of R1, denoted hereafter as k1 (in the unit of cm 3 molecule -1 s -1 if not specified otherwise), show a minimum around 700-800 K. Further, the effect of pressure on k1 is significant at low temperatures, but vanishes at temperatures above 600 K.The aforementioned unique temperature-and pressure-dependent behaviors are related to the properties of R1 potential energy surface (PES), which governs the reaction mechanism, kinetics, and dynamics. Indeed, there exists a relatively stable intermediate between the two HO2 radicals, namely the H2O4 intermediate (the HO2 radical dimer) on the triplet state surface, whose energetics and spectroscopic characterization have also been scrutinized extensively by theory and experiment.…”

mentioning

confidence: 99%

Permutation-Invariant-Polynomial Neural-Network-based Δ-Machine Learn-ing Approach: A Case for the HO2 Self-reaction and its Dynamics Study

2022

Preprint

The potential energy surface (PES) plays a central role in chemistry. As the size of the reaction system increases, it would be more and more difficult to develop its globally accurate full-dimensional PES. One unavoidable difficulty is that it is too expensive to calculate electronic energies of ample configurations for complicated reactions. Δ-machine learning is a highly cost-effective method as only a small number of high-level ab initio energies are required to improve a potential energy surface (PES) fit to a large number of low-level points. Here, we propose a permutation-invariant-polynomial neural-network (PIP-NN)-based Δ-machine learning approach to construct full-dimensional accurate PESs for complicated reactions. The approach is applied to the HO2 + HO2 → H2O2 + O2 reaction, a key process in combustion and atmosphere. The full-dimensional triplet state PES is constructed with a large number of density functional theory (DFT) points, which cover all dynamically relevant regions. Only 14% of the DFT dataset are used to successfully bring the DFT PES to the UCCSD(T)-F12a/AVTZ quality. On this PES of high quality, quasi-classical trajectory (QCT) calculations are performed to study the dynamics of the title reaction. A surprising mode-speciﬁc dynamics is observed, in which exciting a spectator mode leads to significant enhancement of the reactivity at low collision energy. This special mechanism can be attributed to increased attraction potential caused by the excited spectator mode. Such mode specificity may be quite prevalent in free radical reactions involving HO2, which is common in combustion and atmosphere.