UV Resonance Raman Investigation of Pentaerythritol Tetranitrate Solution Photochemistry and Photoproduct Hydrolysis

Abstract

Ultraviolet resonance Raman spectroscopy (UVRR) is being developed for standoff trace explosives detection. To accomplish this, it is important to develop a deep understanding of the accompanying UV excited photochemistry of explosives, as well as the impact of reactions on the resulting photoproducts. In the work here we used 229 nm excited UVRR spectroscopy to monitor the photochemistry of pentaerythritol tetranitrate (PETN) in acetonitrile. We find that solutions of PETN in CDCN photodegrade with a quantum yield of 0.08 ± 0.02, as measured by high performance liquid chromatography (HPLC). The initial step in the 229 nm UV photolysis of PETN in CDCN is cleavage of an O-NO bond to form NO. The accompanying photoproduct is pentaerythritol trinitrate (PETriN), (CHONO)CCHOH formed by photolysis of a single O-NO. The resulting UVRR spectra show a dominant photoproduct band at ∼1308 cm, which derives from the symmetric stretch of dissolved NO. This photoproduct NO is hydrolyzed by trace amounts of water, which downshifts this 1308 cm NO Raman band due to the formation of molecular HNO. The dissociation of HNO to NO in the presence of additional water results in an intense NO- symmetric stretching UVRR band at 1044 cm.

Toward Locard’s Exchange Principle: Recent Developments in Forensic Trace Evidence Analysis

“…Raman spectroscopy allows for noninvasive, instant, and standoff identification of explosive materials and was found to be a practical tool for obtaining qualitative and quantitative information about the examined material. The standoff trace explosives detection using UV resonance Raman spectroscopy was investigated by Gares et al and Hufziger et al , The example of the images in visible light, as well as Raman spectra and Raman images of AN and PETN, can be seen in Figure . More information on this technique can be found in the review article by Gares et al Zapata et al proposed a combination of Raman spectroscopy and LC in order to detect, identify, and quantify residues of explosives and energetic salts found in human handmarks .…”

Deep Ultraviolet Standoff Photoacoustic Spectroscopy of Trace Explosives

“…This coincides with a loss of mass for these analytes, due to the photochemical production of gaseous species that leave the substrate surfaces. 22,23,26 At higher loadings, our PAS signal remains above the background for >14 s even as the analyte loading decreases due to photolysis (Fig. 5a).…”

“…The photochemistry of PETN, TNT, and AN when irradiated with deep UV light were previously studied using resonance Raman spectroscopy. [21][22][23] With 229 nm excitation, PETN in solution undergoes cleavage of the O-NO 2 bonds to form NO 2 dissolved in solution. 22 In the solid state, PETN is expected to produce gaseous NO 2 .…”

“…[21][22][23] With 229 nm excitation, PETN in solution undergoes cleavage of the O-NO 2 bonds to form NO 2 dissolved in solution. 22 In the solid state, PETN is expected to produce gaseous NO 2 . Bykov et al observed that AN in the solid state continuously loses mass with 213 nm excitation without forming any new Raman bands.…”

“…Many explosives also undergo photochemistry when irradiated with deep UV light. [21][22][23][24][25][26] Large photoacoustic responses have been observed for photochemical reactions. 27 As we show here, this provides an additional avenue for signal detection.…”