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We present work detailing the oxidative reactivity of the nerve agent simulant dimethyl methylphosphonate (DMMP) with atomic oxygen using time-resolved in situ reflection−absorption infrared spectroscopy (RAIRS) and Xray photoelectron spectroscopy (XPS). When exposed to a supersonic beam containing O( 3 P) with average translational energy of 0.12 eV, thermally annealed DMMP films (less than 50 layers) on single-crystal Au( 111) are observed to react, likely via hydrogen abstraction, and followed by various secondary reactions with resultant hydroxyl and DMMP-derived radicals. This reaction is accompanied by the appearance of hydrogen bonding interactions with the DMMP phosphoryl (PO) groups on the film surface, and it is also observed to result in both a loss of carbon and an uptake of oxygen by the film. These trends, when considered with the additional thermal stability of reaction products left on the surface, suggest that the mechanism entails reaction with DMMP methyl groups and the formation of various polymeric species; the presence of these polymers hinders continuous, effective destruction for films thicker than roughly ten layers. This work has specific implications for the implementation of plasma-based and oxidative decontamination methods based upon an improved fundamental understanding of the chemistry of the important class of phosphoryl containing molecules.

We present work detailing the destruction of the nerve agent simulant diisopropyl methylphosphonate (DIMP) via rapid laser heating under atmospheric conditions. Following Nd:YAG laser ablation of liquid DIMP deposited on a graphite substrate, both parent and product fragments are transmitted via capillary from an atmospheric chamber to a vacuum chamber containing a high-resolution mass spectrometer. This allows for real-time measurements of product distributions under a variety of temperature and atmospheric conditions. Ex situ Fourier transform infrared (FTIR) spectroscopy analysis of the same chamber contents provides complementary information about product identities and fragmentation pathways. Results demonstrate that product distributions depend on heating rate, surface temperature, and atmospheric oxygen content. In the destruction of the DIMP, the relative yields of alkene products depends significantly on laser power; smaller products are relatively more abundant at higher ablation temperatures. We also show that in the absence of atmospheric oxygen, the concentration of oxygenated products decreases sharply relative to alkene and alkane products. This suggests that under high-temperature conditions, atmospheric oxygen is incorporated directly into the products of the fragmented simulant. This project extends significantly our understanding of the fundamental chemistry of these dangerous compounds under atmospheric and rapidly changing thermal conditions. The results have critical implications for the development of effective chemical warfare agent decontamination and destruction strategies.

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We present research detailing the sticking probability of CH4 on various D2O ices of terrestrial and astrophysical interest using a combination of time-resolved, in situ reflection absorption infrared spectroscopy (RAIRS) and King and Wells mass spectrometry techniques. As the incident translational energy of CH4 increases (up to 1.8 eV), the sticking probability decreases for all ice films studied, which include high-density, non-porous amorphous (np-ASW), and crystalline (CI) films as well as porous amorphous (p-ASW) films with various pore morphologies. Importantly, sticking probabilities for all p-ASW films diverge and remain higher than either np-ASW or CI films at the highest translational energies studied. This trend is consistent across all porous morphologies studied and does not depend on pore size or orientation relative to the substrate. It is proposed that in addition to offering slightly higher binding energies the porous network in the D2O film is very efficient at dissipating the energy of the incident CH4 molecule. These results offer a clear picture of the initial adsorption of small molecules on various icy interfaces; a quantitative understanding of these mechanisms is essential for the accurate modeling of many astrophysical processes occurring on the surface of icy dust particles.