Growth and Decomposition Pathways for Ammonium Nitrate Clusters

The decomposition of ammonium nitrate has important applications in storing and transporting ammonium nitrate safely. Decomposition pathways observed in sputtered mass spectra from literature were explained using binding energies found from Monte Carlo geometry optimizations followed by ωB97X-D3 and ωB97M-V density functional theory calculations. It was found that decomposition of cluster ions due to the loss of ammonia or nitric acid are favored. Additionally, all peaks in the positive and negative mass spectra were identified with their corresponding structures. With the reasonable confidence gained from consistency with experiment, the neutral series (NH₄NO₃)_n was studied for n ≤ 40 in hopes to learn about the early stages of particle growth. This led to an interesting pattern being observed in the structures. Better understanding new particle formation can lead to a better ability to model haze formation in polluted urban environments and model the global climate.