Clusteromics II: Methanesulfonic Acid–Base Cluster Formation

Abstract

The role of methanesulfonic acid (MSA) in atmospheric new particle formation remains highly uncertain. Using state-of-the-art computational methods, we study the electrically neutral (MSA) 0−2 (base) 0−2 clusters, with base = ammonia (A), methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), and ethylenediamine (EDA). The cluster configurations are obtained using the ABCluster program and the number of initial cluster configurations is reduced based on PM7 calculations. Thermochemical parameters are calculated using the quasi-harmonic approximation based on the ωB97X-D/6-31++G(d,p) cluster structures and vibrational frequencies. The single point energies are calculated at the DLPNO-CCSD(T 0 )/aug-cc-pVTZ level of theory. We find that MSA shows a different interaction pattern with the bases compared to sulfuric acid and does not simply follow the basicity of the bases for these small clusters. In all cases, we find that the MSA-base clusters show very low cluster formation potential, indicating that electrically neutral clusters consisting solely of MSA as the clustering acid are most likely not capable of forming and growing under realistic atmospheric conditions.

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

“…Previously, we identified that the SA–TMA system had a high cluster formation potential 50 while the corresponding MSA–TMA system effectively formed zero clusters. 51 This effect was attributed to the emergence of weak S=O···H–C noncovalent interactions due to MSA and TMA only having one donor–acceptor pair available for hydrogen bonding. However, the observed interactions between the SA and MSA molecules in the SA–MSA–base clusters in Figure 1 will likely mitigate the low cluster formation potential observed in the MSA–TMA system.…”

“…The calculations are performed at the DLPNO–CCSD(T 0 )/aug-cc-pVTZ//ωB97X-D/6-31++G(d,p) level of theory using the quasi-harmonic approximation. The corresponding data for the SA–base 50 and MSA–base 51 systems are presented as a comparison. On the basis of the gas-phase basicity of the base molecules, 79 they are divided into classifications (weak, medium, strong).…”

“… a The base strength classifications are divided into: w = weak, m = medium, and s = strong. b,c Data taken from ref ( 50 ) and ( 51 ), respectively. …”

“…We have previously defined the synergistic effect between two cluster components j and k with the synergy factor Γ j , k : 50 , 51 Hence, the synergy factor for a given cluster composition indicates nonadditive behavior in the thermodynamics. The previous studies investigated the base synergy factors for (SA) 1–2 (base) 1–2 and (MSA) 1–2 (base) 1–2 clusters.…”

“…In our first two clusteromics papers, we studied SA–base 50 and MSA–base 51 clustering. Depending on the basicity of the clustering base, SA–base clusters can rapidly form and grow.…”