We report density functional theory calculations of infrared absorption spectra for the organophosphonate nerve agent sarin and its adsorbed structures on low-energy surfaces of anatase titanium dioxide. The first-principles calculations enable direct association between features of the infrared spectra and the associated vibrational normal modes. We corroborate a well-known red shift in the P=O stretching mode and find that the magnitude of the shift is greater on the (001) surface than the (101) surface, correlated with the energy of adsorption. A consistent blue shift in the P-O-C stretching mode is also observed whose magnitude correlates with energy of adsorption. In addition to the surface model for adsorption, the shifts are predicted using higher levels of theory on small cluster models and are qualitatively consistent. An improved understanding of the mechanisms underlying the band shifts will be useful in experiments monitoring the adsorption and decomposition of sarin and similar molecules.

Vibrational signatures of sarin adsorption on anatase surfaces by density functional theory

2019 Spring National Meeting

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