Density Functional Theory Based Studies on the Nature of Raman and Resonance Raman Scattering of Nerve Agent Bound to Gold and Oxide-Supported Gold Clusters: A Plausible Way of Detection

Abstract

A detailed theoretical investigation has been carried out at the density functional level of theories to investigate the nature of Raman intensities of the -P=O stretching mode of a model nerve agent DFP (diisopropylfluorophosphate) when bound to different gold (Au(8), Au(20)) and oxide-supported gold (MgO...Au(4), CaO...Au(4), TiO(2)...Au(4), Al(2)O(3)...Au(4), M(16)O(16)...Au(8), and [M(16)O(15)...Au(8)](2+), M = Ca, Mg) clusters. All of these clusters and the DFP-bound clusters are fully optimized, and the computed energetics shows that DFP attaches itself weakly to these clusters. The normal Raman spectra calculations on these clusters show that there is substantial enhancement of the -P=O stretching mode of DFP compared to the isolated species. This enhancement has been found to be due to the polarization of the -P=O bond of DFP when bound to the clusters. Significant enhancement in intensity has been observed in the case of Au(n)...DFP (n = 8, 20), M(16)O(16)...Au(8)...DFP, and [M(16)O(15)...Au(8)](2+)...DFP (M = Ca, Mg) clusters. The resonance Raman calculations on the Au(n)...DFP (n = 8, 20) reveals that this enhancement could be made quite large and selective, which is a feature that is unique to the nerve agents and could be used as a property for detecting them.

Multimodal Characterization of Materials and Decontamination Processes for Chemical Warfare Protection

“…Raman spectroscopy has been particularly used in determining the lattice dynamics and crystallinity of several materials, such as carbon-based, , metal oxides, , and polymers. , Raman spectroscopy can also be used in a time-resolved manner to track the structural changes under in situ conditions . In particular, Raman has been useful in identifying structures, vibrational modes and molecular conformations, as well as bond orientations of organophosphorus compounds in their pure form or when adsorbed onto surfaces. − Depending on the excitation energies, laser power, signal-to-noise ratio, and integration time, many fingerprint regions could be distinguished. , For example, Choi et al showed, using principal component analysis applied to Raman spectra, that nerve agents with similar molecular structures can be easily distinguished . Wang et al.…”