Terahertz absorption spectra of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) polymorphs

Interest in terahertz spectroscopy of organic compounds has been driven by its potential utility as a stand-off detection technology for explosives. Much work has focused on identifying the spectral signatures of explosives compounds and understanding the molecular origin of the complex, low-frequency modes in the terahertz regime. We present distinct absorption spectra in the terahertz region for polymorphs of the secondary high explosive 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). For α-HMX, we couple experiments to solid-state density functional perturbation theory (DFPT) calculations, and find excellent agreement. This work underlines the importance of careful sample preparation when examining spectra and comparing experimental work with calculations.