Synergistic effect of glutaric acid and ammonia/amine/amide on their hydrates in the clustering: A theoretical study

The formation of molecular clusters makes influence on the atmosphere. The clusters of glutaric acid (GA) and common ammonia (A), amine (methylamine MA, dimethylamine DMA) and representative amide (urea U) along with water molecule were systematically studied theoretically. GA-A-nW (n = 1, 2), GA-MA-nW (n = 1, 2), GA-DMA-1W and GA-U-nW (n = 1–6) are predicted to be feasible thermodynamically with the hydrogen bonds as interaction force. GA and urea promote the clustering synergistically, and ammonia, methylamine, dimethylamine promote the clustering of small GA hydrates (n = 1–2), while inhibit that of large GA hydrates (n = 3–6). The results of humidity show that un-hydrate or mono-hydrate is the main form of GA-mbase-nW (m = 0, 1; n = 1–6) under relative humidity of 20%, 50% and 80%. The global minima remain dominant over the temperature range of 220–320 K. GA contributes more to the Rayleigh scattering properties than sulfuric acid. More importantly, the local minima can undergo isomerization to form the global minima crossing a free energy barrier ranging from 6.66 to 11.78 kcal mol−1. This study indicates that GA and base molecules play a synergistic role to promote the formation of clusters. We hope it can provide more insights on interesting clustering in theory.