Visible and UV resonance Raman spectroscopy of the peroxide-based explosive HMTD and its photoproducts

Abstract

Hexamethylene triperoxide diamine (HMTD) is a peroxide-based explosive that is easily manufactured from household chemicals. This high-energy molecule is challenging to detect because it lacks the characteristic –NO2 functional group that is the primary target of modern detection devices. One tool that is well-suited for detection and characterization of HMTD and other peroxide explosives is Raman spectroscopy. Off-resonance Raman spectra with 514.5nm excitation of HMTD and its 13C and 15N isotopologues are presented here. These experimental results are compared to calculations to reveal the vibrational structure and normal mode assignments of this strained molecule. Intense peaks that reflect global torsional motion appear in the low-frequency region (<700cm−1), and the dominant peroxide O–O stretch appears at 773cm−1. UV resonance Raman (UVRR) spectra with 228nm excitation show signatures of the photodegradation products of HMTD. These photoproducts, including those of the isotopologues, are identified via mass spectrometry and vibrational analysis. We hypothesize that upon absorption of UV light, one or more O–O bond is cleaved, resulting in the release of formaldehyde and O2. Subsequent reactions create an imide product that has a strong band in the UVRR spectrum centered at 1736cm−1. These results highlight the benefits of off- and on-resonance Raman spectroscopy as detection tools for HMTD and its photoproducts.