Edgewood, MD, United States
Edgewood, MD, United States

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PubMed | Virginia Polytechnic Institute and State University, Research and Technology Directorate and EXCET Inc.
Type: Journal Article | Journal: The journal of physical chemistry letters | Year: 2015

Sarin and soman are warfare nerve agents that represent some of the most toxic compounds ever synthesized. The extreme risk in handling such molecules has, until now, precluded detailed research into the surface chemistry of agents. We have developed a surface science approach to explore the fundamental nature of hydrogen bonding forces between these agents and a hydroxylated surface. Infrared spectroscopy revealed that both agents adsorb to amorphous silica through the formation of surprisingly strong hydrogen-bonding interactions with primarily isolated silanol groups (SiOH). Comparisons with previous theoretical results reveal that this bonding occurs almost exclusively through the phosphoryl oxygen (PO) of the agent. Temperature-programmed desorption experiments determined that the activation energy for hydrogen bond rupture and desorption of sarin and soman was 50 2 and 52 2 kJ/mol, respectively. Together with results from previous studies involving other phosphoryl-containing molecules, we have constructed a detailed understanding of the structure-function relationship for nerve agent hydrogen bonding at the gas-surface interface.

Guicheteau J.A.,Research and Technology Directorate | Swofford H.,U.S. Army | Tripathi A.,SAIC | Wilcox P.G.,Research and Technology Directorate | And 4 more authors.
Journal of Forensic Identification | Year: 2013

Through a collaborative effort between the United States Army Edgewood Chemical Biological Center (ECBC) and the United States Army Criminal Investigation Laboratory (USACIL), the ability to perform sequential Raman chemical imaging (RCI) and biometric analysis on fingerprints for rapid identification of threat materials and individuals was demonstrated. The chemical analysis and imaging of the fingerprints are achieved simultaneously through RCI. The fingerprint image, which bears the location and identity of the threat materials embedded within the fingerprint residue, is also suitable for subsequent biometric analysis through an automated fingerprint identification system (AFIS). In our tests, AFIS consistently generated a candidate list containing the source of the fingerprint in the top ranking position. These results mark the first step towards the practical application and implementation of RCI for chemical and biometric analyses on fingerprints routinely obtained at security checkpoints or developed during forensic counter-terrorism and drug investigations.

Tripathi A.,SAIC | Emmons E.D.,National Research Council at the Research and Technology Directorate | Wilcox P.G.,Research and Technology Directorate | Guicheteau J.A.,Research and Technology Directorate | And 3 more authors.
Applied Spectroscopy | Year: 2011

We have previously demonstrated the use of wide-field Raman chemical imaging (RCI) to detect and identify the presence of trace explosives in contaminated fingerprints. In this current work we demonstrate the detection of trace explosives in contaminated fingerprints on strongly Raman scattering surfaces such as plastics and painted metals using an automated background subtraction routine. We demonstrate the use of partial least squares subtraction to minimize the interfering surface spectral signatures, allowing the detection and identification of explosive materials in the corrected Raman images. The resulting analyses are then visually superimposed on the corresponding bright field images to physically locate traces of explosives. Additionally, we attempt to address the question of whether a complete RCI of a fingerprint is required for trace explosive detection or whether a simple non-imaging Raman spectrum is sufficient. This investigation further demonstrates the ability to nondestructively identify explosives on fingerprints present on commonly found surfaces such that the fingerprint remains intact for further biometric analysis. © 2011 Society for Applied Spectroscopy.

Wilmsmeyer A.R.,Virginia Polytechnic Institute and State University | Gordon W.O.,Research and Technology Directorate | Davis E.D.,OptiMetrics, Inc. | Troya D.,Virginia Polytechnic Institute and State University | And 3 more authors.
Journal of Physical Chemistry C | Year: 2013

The fundamental interactions of a series of chemical warfare agent (CWA) simulants on amorphous silica particulates have been investigated with transmission infrared spectroscopy and temperature-programmed desorption (TPD). The simulants methyl dichlorophosphate (MDCP), dimethyl cholorophosphate (DMCP), trimethyl phosphate (TMP), dimethyl methylphosphonate (DMMP), and diisopropyl methylphosphonate (DIMP) were chosen to help develop a comprehensive understanding for how the structure and functionality of CWA surrogate compounds affect uptake and hydrogen-bond strengths at the gas-surface interface. Each simulant was found to adsorb molecularly to silica through the formation of strong hydrogen bonds primarily between isolated surface silanol groups and the oxygen atom of the P=O moiety in the adsorbate. The TPD data revealed that the activation energy for desorption of a single simulant molecule from amorphous silica varied slightly with coverage. In the limit of zero coverage and the absence of significant surface defects, the activation energies for desorption were found to follow the trend MDCP < DMCP < TMP < DMMP < DIMP. This trend demonstrates the critical role of electron-withdrawing substituents in determining the adsorption energies through hydrogen-bonding interactions. The infrared spectra for each adsorbed species, recorded during uptake, showed a significant shift in the frequency of the ν(SiO-H) mode as the hydrogen bonds formed. A clear linear relationship between the desorption energy and the shift of the surface ν(SiO-H) mode across this series of adsorbates demonstrates that the Badger-Bauer relationship, established origninally for solute-solvent interactions, effectively extends to gas-surface interactions. High-level electronic structure calculations, including extrapolation to the complete basis set limit, reproduce the experimental energies of all simulants with high levels of accuracy and have been employed to provide insight into the molecular-level details of adsorption geometries for the simulants and to predict the interaction energies for the CWA isopropyl methylphosphonofluoridate (sarin). © 2013 American Chemical Society.

Kunz R.R.,Lincoln Laboratory | Gregory K.E.,Lincoln Laboratory | Aernecke M.J.,Lincoln Laboratory | Clark M.L.,Lincoln Laboratory | And 2 more authors.
Journal of Physical Chemistry A | Year: 2012

The chemical and physical fates of trace amounts (<50 Îg) of explosives containing 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3, 5-triazine (RDX), and pentaerythritol tetranitrate (PETN) were determined for the purpose of informing the capabilities of tactical trace explosive detection systems. From these measurements, it was found that the mass decreases and the chemical composition changes on a time scale of hours, with the loss mechanism due to a combination of sublimation and photodegradation. The rates for these processes were dependent on the explosive composition, as well as on both the ambient temperature and the size distribution of the explosive particulates. From these results, a persistence model was developed and applied to model the time dependence of both the mass and areal coverage of the fingerprints, resulting in a predictive capability for determining fingerprint fate. Chemical analysis confirmed that sublimation rates for TNT were depressed by UV (330-400 nm) exposure due to photochemically driven increases in the molecular weight, whereas the opposite was observed for RDX. No changes were observed for PETN upon exposure to UV radiation, and this was attributed to its low UV absorbance. © 2012 American Chemical Society.

Emge D.K.,Research and Technology Directorate | Guicheteau J.A.,Research and Technology Directorate
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Surface enhanced Raman Scattering spectroscopy is a valuable tool for detecting and identifying chemical threats. One difficulty, however, in utilizing its full capabilities is that the spectrum is dependent upon the chemical orientation, and to a lesser extent, concentration. Spectral peaks can shift and even disappear as the concentration of the chemical present varies. A potential solution to this problem is to model the spectrum as a set of random basis functions, with each basis function depending upon a random unobserved parameter. Relating these parameters to the concentration an expected least squares fitting procedure can be implemented. It is shown through computer simulation and some limited testing that the detection and classification performance can be improved over standard approaches that do not take into account this basis variation. The method proposed, however, is completely general. It is a viable alternative to standard least squares procedures whenever the goal is robustness of the procedure. © 2012 SPIE.

Tripathi A.,SAIC | Emmons E.D.,SAIC | Christesen S.D.,Research and Technology Directorate | Fountain A.W.,Research and Technology Directorate | Guicheteau J.A.,Research and Technology Directorate
Journal of Physical Chemistry C | Year: 2013

Thiophenol is commonly used as a model system for surface-enhanced Raman scattering (SERS) of molecules due to the strong affinity of the-SH group toward noble metal surfaces. By performing time-, temperature-, and pH-dependent measurements of thiophenol adsorption on commercial nanostructured gold SERS substrates, we have observed both physisorption and chemisorption processes. These two distinct adsorption regimes were found dependent on the pH which controlled the ionization state of thiophenol in an aqueous medium. At low pH the sulfhydryl proton remains bound, and the kinetic adsorption profile obtained from the SERS intensity follows a sigmoid-shaped curve with an initially slow adsorption rate that deviates from a Langmuir profile. In addition, from temperature-dependent measurements, a near zero value for the activation energy is obtained, indicating that physisorption is the rate-limiting step. At high pH, where the sulfhydryl proton becomes detached, the kinetic adsorption profile follows a classical Langmuir profile, and the activation energy is significantly higher than at low pH, indicating that chemisorption is the rate-limiting step. © 2013 American Chemical Society.

Emmons E.D.,SAIC | Guicheteau J.A.,Research and Technology Directorate | Fountain III A.W.,Research and Technology Directorate | Christesen S.D.,Research and Technology Directorate
Applied Spectroscopy | Year: 2012

Raman cross-sections of explosives in solution and in the solid state have been measured using visible and near-infrared excitation via secondary calibration. These measurements are valuable for both fundamental scientific purposes and applications in the standoff detection of explosives. The explosive compounds RDX, HMX, TNT, 2,4-DNT, 2,6-DNT, and ammonium nitrate were measured using discrete excitation wavelengths ranging from 532 nm to 785 nm. A comparison of the spectral features and cross-sections between the solid state and solution was performed. Comparison is also made to cross-sections measured with deep ultraviolet excitation. © 2012 Society for Applied Spectroscopy.

Emmons E.D.,SAIC | Tripathi A.,SAIC | Guicheteau J.A.,Research and Technology Directorate | Fountain A.W.,Research and Technology Directorate | Christesen S.D.,Research and Technology Directorate
Journal of Physical Chemistry A | Year: 2013

Resonance Raman cross sections of common explosives have been measured by use of excitation wavelengths in the deep-UV from 229 to 262 nm. These measurements were performed both in solution and in the native solid state for comparison. While measurements of UV Raman cross sections in solution with an internal standard are straightforward and commonly found in the literature, measurements on the solid phase are rare. This is due to the difficulty in preparing a solid sample in which the molecules of the internal standard and absorbing analyte/explosive experience the same laser intensity. This requires producing solid samples that are mixtures of strongly absorbing explosives and an internal standard transparent at the UV wavelengths used. For the solid-state measurements, it is necessary to use nanostructured mixtures of the explosive and the internal standard in order to avoid this bias due to the strong UV absorption of the explosive. In this study we used a facile spray-drying technique where the analyte of interest was codeposited with the nonresonant standard onto an aluminum-coated microscope slide. The generated resonance enhancement profiles and quantitative UV-vis absorption spectra were then used to plot the relative Raman return as a function of excitation wavelength and particle size. © 2013 American Chemical Society.

PubMed | Research and Technology Directorate
Type: Journal Article | Journal: Applied spectroscopy | Year: 2013

We present the results of a three-year collaboration between the U.S. Army Edgewood Chemical Biological Center and the U.S. Army Research Laboratory-Aldelphi Laboratory Center on the evaluation of selected nanometallic surfaces developed for the Defense Advanced Research Projects Agency Surface-Enhanced Raman Scattering (SERS) Science and Technology Fundamentals program. The primary role of the two Army labs was to develop the analytical and spectroscopic figures of merit to unambiguously compare the sensitivity and reproducibility of various SERS substrates submitted by the program participants. We present the design and implementation of an evaluation protocol for SERS active surfaces enabling an enhancement value calculation from which different substrates can be directly compared. This method was established to: (1) collect physical and spectral characterization data from the small number of substrates (performer supplied) typically encountered, and (2) account for the complex fabrication technique and varying nature of the substrate platforms encountered within this program.

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