Oxidative Destruction of Multilayer Diisopropyl Methylphosphonate Films by O(³P) Atomic Oxygen

Abstract

We present work detailing the oxidative destruction of the nerve agent simulant diisopropyl methylphosphonate (DIMP) with O(P) using time-resolved, in situ reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). Thermally annealed DIMP films deposited on Au(111) are observed to react upon exposure to a supersonic beam containing O(P) with average translational energies of 0.12 eV. The reaction is initiated by a hydrogen abstraction from one of three possible sites on DIMP, and then progresses through various secondary reactions with resultant hydroxyl radicals, carbon-centered DIMP-derived radicals, and nondissociated O in the beam. These reactions are accompanied by uptake of oxygen into the film, leading to new hydrogen bonding with the DIMP phosphoryl group. The generated product also presents greater thermal stability than pristine DIMP, suggesting the formation of a distribution of oligomeric and polymeric products. As reactivity is observed to decrease upon continued O(P) exposure, this product likely forms a protective layer at the vacuum-film interface, hindering destruction of thicker films. Importantly, the rate of reaction and general reactivity trends are the same between DIMP and the smaller simulant dimethyl methylphosphonate (DMMP). The comparable reaction rates of the two molecules coupled with oxygen's inability to erode thick films all the way down to the substrate have specific implications for the development of oxidation-based decontamination strategies for these and other organophosphates in the solid phase. The findings presented in this paper add significant new fundamental understanding of the oxidative chemistry of such species, knowledge needed in order to develop efficacious nerve agent decontamination strategies as well as the refinement of existing models for the dispersal, adsorption, persistence, and destruction of organophosphates in the environment.

Rapid Laser-Induced Temperature Jump Decomposition of the Nerve Agent Simulant Diisopropyl Methylphosphonate under Atmospheric Conditions

“…In addition to experimental and theoretical work on the thermal decomposition and combustion of these compounds, 11,17,19−21 this work is an extension of previous studies examining oxidative 22,23 and laser destruction 24 of adsorbed chemical nerve agent simulants under ultrahigh vacuum conditions. The oxidative destruction of DIMP and dimethyl methylphosphonate (DMMP) progresses at similar rates and yields oxygen-and carbonyl-containing oligomeric product species.…”

“…In addition to experimental and theoretical work on the thermal decomposition and combustion of these compounds, ,,− this work is an extension of previous studies examining oxidative , and laser destruction of adsorbed chemical nerve agent simulants under ultrahigh vacuum conditions. The oxidative destruction of DIMP and dimethyl methylphosphonate (DMMP) progresses at similar rates and yields oxygen- and carbonyl-containing oligomeric product species. , Laser desorption and destruction studies of a number of Sarin simulants, (DIMP, DMMP, and diethyl ethylphosphonate), demonstrated lower temperature thresholds for destruction of simulants with relatively larger phosphonate side chains . On the basis of these results, we again expect that the majority of gas-phase products in this study will include a variety of 1, 2, and 3-carbon products generated from the DIMP isopropyl group, with possible incorporation of atmospheric oxygen.…”

“…The oxidative destruction of DIMP and dimethyl methylphosphonate (DMMP) progresses at similar rates and yields oxygen-and carbonyl-containing oligomeric product species. 22,23 Laser desorption and destruction studies of a number of Sarin simulants, (DIMP, DMMP, and diethyl ethylphosphonate), demonstrated lower temperature thresholds for destruction of simulants with relatively larger phosphonate side chains. 24 On the basis of these results, we again expect that the majority of gas-phase products in this study will include a variety of 1, 2, and 3-carbon products generated from the DIMP isopropyl group, with possible incorporation of atmospheric oxygen.…”