Clusteromics II: Methanesulfonic Acid–Base Cluster Formation

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(T0)/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.