Isotopic Substitution in Energetic Materials Facilitates Understanding of Decomposition Mechanisms in Abnormal Thermal Environments*

Isotopic substitution (IS) is a powerful tool to assess the decomposition of energetic materials (EMs).  IS is replacement of naturally occurring atoms with single isotope atoms having specific probe properties.  With this replacement, molecular level decomposition can be delineated and changes in global behavior can be better understood utilizing the kinetic isotope effect.  For most EMs, conquering several tasks are required: 1) developing synthetic methods to produce labeled analogues comparable to the unlabeled EM, 2) finding isotopically labeled precursors, and, 3) recruiting skillful synthesis personnel.  Substitutions of interest for many EMs are ¹⁵N for nitro and amino groups, ¹⁸O for nitro groups, ²H for protonated sites and ¹³C for carbon skeleton.  As the EM thermally decomposes, these isotopic labels end up in isotopically labeled gases, liquids, and solids.  Analyses methods utilized are mass spectrometry (MS)—shift in mass values; nuclear magnetic resonance (NMR) spectroscopy—environments around specific nuclei; Infrared/Raman spectroscopy—fingerprint vibrations of functional groups.  Our understanding of molecular processes and global behavior in thermal decomposition through IS labeling has been greatly advanced.  This presentation will show some impressive results about the molecular pathways for specific insensitive high explosives and global reaction behavior unrealized until now.  Also, discussion of the concept of deflagration-to-detonation (DDT) will be discussed.