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

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 CD 3 CN 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 CD 3 CN is cleavage of an O-NO 2 bond to form NO 2 . The accompanying photoproduct is pentaerythritol trinitrate (PETriN), (CH 2 ONO 2 ) 3 CCH 2 OH formed by photolysis of a single O-NO 2 . The resulting UVRR spectra show a dominant photoproduct band at ∼1308 cm –1, which derives from the symmetric stretch of dissolved NO 2 . This photoproduct NO 2 is hydrolyzed by trace amounts of water, which downshifts this 1308 cm –1 NO 2 Raman band due to the formation of molecular HNO 3 . The dissociation of HNO 3 to NO 3 – in the presence of additional water results in an intense NO 3 - symmetric stretching UVRR band at 1044 cm –1 .