Hydrogen-Bond Topology Is More Important Than Acid/Base Strength in Atmospheric Prenucleation Clusters

Abstract

We explored the hypothesis that on the nanoscale level, acids and bases might exhibit different behavior than in bulk solution. Our study system consisted of sulfuric acid, formic acid, ammonia, and water. We calculated highly accurate Domain-based Local pair-Natural Orbital- Coupled-Cluster/Complete Basis Set (DLPNO-CCSD­(T)/CBS) energies on DFT geometries and used the resulting Gibbs free energies for cluster formation to compute the overall equilibrium constants for every possible cluster. The equilibrium constants combined with the initial monomer concentrations were used to predict the formation of clusters at the top and the bottom of the troposphere. Our results show that formic acid is as effective as ammonia at forming clusters with sulfuric acid and water. The structure of formic acid is uniquely suited to form hydrogen bonds with sulfuric acid. Additionally, it can partner with water to form bridges from one side of sulfuric acid to the other, hence demonstrating that hydrogen bonding topology is more important than acid/base strength in these atmospheric prenucleation clusters.

Clusteromics III: Acid Synergy in Sulfuric Acid–Methanesulfonic Acid–Base Cluster Formation

“…In a similar manner, because of its high abundance, formic acid was recently shown to be the most efficient organic acid in enhancing MSA–MA cluster formation. 82 Furthermore, by studying small clusters consisting of sulfuric acid, formic acid, ammonia, and water, Harold et al 83 recently showed that formic acid is just as effective as ammonia in stabilizing the clusters. Hence, further studies on the role of nitric acid and formic acid in cluster formation is warranted.…”

Clusteromics IV: The Role of Nitric Acid in Atmospheric Cluster Formation

“… 84 Formic acid has furthermore been shown to be just as effective as ammonia in stabilizing small clusters containing sulfuric acid, formic acid, ammonia, and water. 85 Hence, further studies on the role of formic acid in cluster formation are warranted.…”

The driving effects of common atmospheric molecules for formation of prenucleation clusters: the case of sulfuric acid, formic acid, nitric acid, ammonia, and dimethyl amine

“…Clusters containing SA, FA, A, and W were previously optimized with the M08-HX functional and the MG3S basis set. 68,100 All of these M08-HX geometries were re-optimized with uB97X-D using the 6-31++G** basis set [103][104][105][106] to obtain a nal set of consistent geometries. The electronic energies of all structures within 8 kcal mol −1 of the uB97X-D global minimum for each system were recomputed using the domain-based local pair natural orbital coupled-cluster (DLPNO-CCSD(T)) method [107][108][109][110][111][112][113][114][115][116][117][118][119][120] with single, double, and semi-canonical perturbative triple excitations with three Dunning basis sets, cc-pVnZ (n ¼ D, T, Q), [121][122][123][124] using the ORCA 5.0.1 program.…”

“…Rasmussen et al (SA) 3 (W) n were both calculated using uB97X-D for the geometry optimizations and DLPNO-CCSD(T) for the single-point energy calculations while the Zhu et al (SA) 2 (acetic acid)(W) n system was calculated using PW91PW91 for both geometries and energies. Differences in these methodologies could explain the discrepancy for when ionization occurs in these systems, as quite oen the DLPNO-CCSD(T)/CBS minimum differs from the DFT minimum for atmospheric clusters 58,59,68. 3.5 Tetramers of three acids and one base…”