Diisopropyl Methylphosphonate and Sarin Decomposition on Pristine vs. Hydroxylated Alumina Surfaces: Mechanistic Predictions from Ab Initio Molecular Dynamics

Understanding the reactivity of chemical warfare agents on material surfaces is essential for mitigating and controlling their chemical/biological activity. Using \textit{ab initio} molecular dynamics, we compare the adsorption and decomposition of sarin and its simulant, diisopropyl methylphosphonate (DIMP), on both pristine and hydroxylated alumina surfaces at various temperatures. Our extensive calculations confirm that DIMP is a suitable simulant for sarin experimental studies on pristine alumina surfaces due to their similar adsorption configurations and reaction dynamics. Moreover, our ab initio molecular dynamics simulations predict C--O bond cleavage to be the initial decomposition step for both DIMP and sarin on the pristine surface. We also identify an additional potential decomposition route for sarin via cleavage of the P--F bond. While similarities exist on the pristine surface, differences between sarin and DIMP emerge on the hydroxylated surface at elevated temperatures. This work provides detailed insights into these atomistic decomposition mechanisms and highlights the utility of predictive quantum dynamics simulations for evaluating the suitability of simulants to guide future experimental investigations of these hazardous compounds.