Theoretical study on reaction mechanism of sulfuric acid and ammonia and hydration of (NH4)2SO4

Liu, Weiwei; Wang, Xiaolin; Chen, Shi-Lu; Zhang, Yunhong; Li, Ze-Sheng

doi:10.1007/s00214-012-1103-4

Cited by 5 publications

(2 citation statements)

References 50 publications

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“…The same study also notes that while there may be differences between the static and dynamic results, the equilibrium picture of cluster formation is similar for the two approaches. Similarly, Liu et al used DFT-based FPMD to explore cluster formation in uncharged ammonium sulfate clusters and found that activation barriers of similar height exist for the addition of two ammonia molecules to a sulfuric acid molecule without water.…”

Section: Resultsmentioning

confidence: 99%

Activation Barriers in the Growth of Molecular Clusters Derived from Sulfuric Acid and Ammonia

DePalma

Bzdek²,

Ridge

et al. 2014

J. Phys. Chem. A

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Unraveling the chemical mechanism of atmospheric new particle formation (NPF) has important implications for the broader understanding of the role of aerosols in global climate. We present computational results of the transition states and activation barriers for growth of atmospherically relevant positively charged molecular clusters containing ammonia and sulfuric acid. Sulfuric acid uptake onto the investigated clusters has a small activation free-energy barrier, consistent with nearly collision-limited uptake. Ammonia uptake requires significant reorganization of ions in the preexisting cluster, which yields an activation barrier on the order of 29−53 kJ/mol for the investigated clusters. For this reason, ammonia uptake onto positively charged clusters may be too slow for cluster growth to proceed by the currently accepted mechanism of stepwise addition of sulfuric acid followed by ammonia. The results presented here may have important implications for modeling atmospheric NPF and nanoparticle growth, which typically does not consider an activation barrier along the growth pathway and usually assumes collision-limited molecular uptake. ■ INTRODUCTIONAtmospheric new particle formation (NPF) is a gas-to-particle conversion process that influences the concentration of ambient particulate matter. 1 While the chemical mechanisms of NPF have not been fully elucidated, important species include sulfuric acid, 2−4 water, bases 5−8 (such as ammonia and amines), and carbonaceous matter. 9−12 The structures and reactivities of the molecular clusters driving NPF have been the focus of experimental and theoretical investigations, 13−28 and both approaches have provided valuable insight into the chemical mechanisms underlying particle formation. In order to effectively model both the correct formation pathway as well as the rate of particle formation, energetic barriers must be considered. In the few modeling studies of cluster growth energetics, 28,29 the barriers explored have been only thermodynamic barriers, that is, the Gibbs free-energy difference between a product cluster and the reactant species. To our knowledge, the direct transition states (TSs) between reactant and product clusters have not been explored. If an activation barrier must be traversed when going from reactant to product, it will impact both the pathways and rates of cluster growth.Our research group has studied the formation and reactivity of clusters between sulfuric acid and a base (ammonia or amine) using a combination of experimental and computational approaches. 30−36 In recent experimental work, we explored the kinetics and energetics of the fragmentation of charged ammonium bisulfate clusters using Fourier transform ion cyclotron resonance mass spectrometry in order to elucidate possible cluster growth mechanisms. 31 On the basis of the assumption that cluster growth is the reverse of cluster fragmentation, activation barriers were found to exist for the addition of ammonia to charged clusters but not for the addition of sulfuric acid (i.e.,...

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Section: Resultsmentioning

confidence: 99%

Activation Barriers in the Growth of Molecular Clusters Derived from Sulfuric Acid and Ammonia

DePalma

Bzdek²,

Ridge

et al. 2014

J. Phys. Chem. A

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show abstract

“…Because a binary mixture of water and sulfuric acid at relevant atmospheric concentrations is insufficient to explain the magnitude of observed nucleation rates and the large scatter between different observation sites, other chemical compounds have been implicated. Bases such as ammonia, amines, or aromatic nitrogen-containing heterocycles are the strongest candidates to contribute to the nucleation process; consequently, they have been the focus of recent experimental and computational investigations. − The particle formation process can be clarified by computing formation free energies (relative to the monomers) for a range of cluster sizes and compositions. Furthermore, these free energies can be used to estimate the evaporation and fragmentation rates of the clusters.…”

Section: Introductionmentioning

confidence: 99%

Energetics of Atmospherically Implicated Clusters Made of Sulfuric Acid, Ammonia, and Dimethyl Amine

et al. 2013

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The formation of atmospheric aerosol particles through clustering of condensable vapors is an important contributor to the overall concentration of these atmospheric particles. However, the details of the nucleation process are not yet well understood and are difficult to probe by experimental means. Computational chemistry is a powerful tool for gaining insights about the nucleation mechanism. Here, we report accurate electronic structure calculations of the potential energies of small clusters made from sulfuric acid, ammonia, and dimethylamine. We also assess and validate the accuracy of less expensive methods that might be used for the calculation of the binding energies of larger clusters for atmospheric modeling. The PW6B95-D3 density-functional-plus-molecular-mechanics calculation with the MG3S basis set stands out as yielding excellent accuracy while still being affordable for very large clusters.

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Optical properties of silver and copper clusters with up to 150 atoms

Grigoryan

Springborg

Minassian

et al. 2013

Computational and Theoretical Chemistry

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Theoretical study on reaction mechanism of sulfuric acid and ammonia and hydration of (NH4)2SO4

Cited by 5 publications

References 50 publications

Activation Barriers in the Growth of Molecular Clusters Derived from Sulfuric Acid and Ammonia

Activation Barriers in the Growth of Molecular Clusters Derived from Sulfuric Acid and Ammonia

Energetics of Atmospherically Implicated Clusters Made of Sulfuric Acid, Ammonia, and Dimethyl Amine

Optical properties of silver and copper clusters with up to 150 atoms

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