Untangling the Reaction Mechanisms Involved in the Decomposition of Nitramine-Based Energetic Materials in the Condensed Phase


The primary objectives of this project are to explore experimentally the mechanisms involved in the decomposition of key representatives of nitramine-based energetic materials (RRN–NO2; RDX, HMX, CL-20) in the condensed phase (solid state) and to identify the primary and higher-order reaction products, among them carbon-, nitrogen-, and oxygen-centered radicals, which are formed in these processes. This presents a major experimental challenge since no comprehensive study has been conducted to date, in which the decomposition mechanisms of nitramine-based energetic materials and the overall spectrum of newly formed open and closed shell products have been explored on line and in situ in the condensed phase. These data are very much required by the energetic material community to unravel the mechanisms and bond breaking processes, which trigger the decomposition of energetic molecules and ‘switch on’ the supply of radicals in the decomposition. These objectives are achieved by systematically initiating the decomposition of the nitramines in the condensed phase by ‘pumping’ energy into these molecules via infrared multiphoton dissociation (IRMPD) and single photon ultraviolet photodissociation (UVPD) while tracing the products formed in these processes in an ultra-high vacuum machine. Our experimental setup incorporates highly complementary detection schemes to monitor these processes on line and in situ within the solid state (Fourier Transform Infrared (FTIR), Raman, ultraviolet-visible (UV-VIS) spectroscopy) and by detecting the products subliming into the gas phase via single vacuum ultraviolet (VUV) photon soft ionization (PI) followed by a mass spectroscopic analysis of the ions in a reflectron time-of-flight mass spectrometer (ReTOF-MS) to reveal the complex dissociation processes of nitramine-based energetic materials comprehensively.

Structures of RDX (cyclotrimethylenetrinitramine), HMX (cyclotetramethylenetetranitramine), CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexa-azaisowurtzitane).

By initiating the decomposition of three key representatives of nitramine-based energetic materials via IRMPD and UVPD and following the formation of new molecules on line and in situ, we extract versatile concepts on the reaction mechanisms, products and their branching ratios, and intermediates in the decomposition of nitramine-based energetic materials. Besides the basic scientific interest from the energetic materials community, these studies are also of fundamental interest to the physical (organic) chemistry community to unravel fundamental decomposition mechanisms of complex organic molecules, to probe isomerization processes of organic transient species on electronic ground and excited state surfaces, and to correlate distinct fragmentation mechanisms with the molecular structure of the molecule thus ultimately providing a systematic understanding and key concepts of the decomposition of nitramine-based energetic materials in the condensed phase.

Top view of the experimental setup including analytical devices.
Overview of W.M. Keck Research Laboratory in Astrochemistry.

Recent Selected Publications

1.   P. Maksyutenko, L.G Muzangwa, B.M. Jones, R.I. Kaiser, Lyman α Photolysis of Solid Nitromethane (CH3NO2) and D3-Nitromethane (CD3NO2) - Untangling the Reaction Mechanisms Involved in the Decomposition of Model Energetic Materials, Phys. Chem. Chem. Phys. 17, 7514 - 7527  (2015).   (PDF)

2.   R.I. Kaiser, P. Maksyutenko, A Mechanistical Study on Non-Equilibrium Reaction Pathways in Solid Nitromethane (CH3NO2) and D3-nitromethane (CD3NO2) upon Interaction with Ionizing Radiation, Chem. Phys. Lett. 631-632, 59-65  (2015).   (PDF)

3.   R.I. Kaiser, P. Maksyutenko, Novel Reaction Mechanisms Pathways in the Electron Induced Decomposition of Solid Nitromethane (CH3NO2) and D3- Nitromethane (CD3NO2), J. Phys. Chem. C 119, 14653-14668  (2015).   (PDF)

4.   M. Förstel, P. Maksyutenko, B.M. Jones, B-J Sun, S-H Chen, A.H.H. Chang, R.I. Kaiser, Detection of the Elusive Triazane Molecule (N3H5) in the Gas Phase, Chem. Phys. Chem. 16, 3139-3142  (2015).   (PDF)

5.   Y.A. Tsegaw, W. Sander, R.I. Kaiser, Electron Paramagnetic Resonance Spectroscopic Study on Nonequilibrium Reaction Pathways in the Photolysis of Solid Nitromethane (CH3NO2) and D3-Nitromethane (CD3NO2), J. Phys. Chem. A. 120, 1577-1587  (2016).   (PDF)

6.   P. Maksyutenko, M. Förstel, P. Crandall, B-J Sun, M.H. Wu, A.H.H. Chang, R.I. Kaiser, An isomer-specific study of solid nitromethane decomposition pathways - Detection of aci-nitromethane (H2CNO(OH)) and nitrosomethanol (HOCH2NO) intermediates, Chem. Phys. Lett., 658, 20-29  (2016).   (PDF)

7.   M. Förstel, Y.A. Tsegaw, P. Maksyutenko, A.M. Mebel, W. Sander, R.I. Kaiser, On the Formation of N3H3 Isomers in Irradiated Ammonia Bearing Ices: Triazene (H2NNNH) or Triimide (HNHNNH), Chem. Phys. Chem. 17, 2726-2735  (2016).   (PDF)

8.   S. Góbi, Parker B. Crandall, P. Maksyutenko, M. Förstel, R.I. Kaiser, Accessing the Nitromethane (CH3NO2) Potential Energy Surface in Methanol (CH3OH)–Nitrogen Monoxide (NO) Ices Exposed to Ionizing Radiation: An FTIR and PI-ReTOF-MS Investigation, J. Phys. Chem. A 122, 2329-2343  (2018).   (PDF)

9.   S. K. Singh, C. Zhu, V. Vuppuluri, S. F. Son, R. I. Kaiser, Probing the Reaction Mechanisms Involved in the Decomposition of Solid 1,3,5-Trinitro-1,3,5-triazinane by Energetic Electrons, J. Phys. Chem. A 123, 9479-9497 (2019).   (PDF)

10.   S. K. Singh, J. L. Jeunesse, V. Vuppuluri, S. F. Son, B. J. Sun, Y. L. Chen, A. H. H. Chang, A. M. Mebel, R. I. Kaiser The Elusive Ketene (H2CCO) Channel in the Infrared Multiphoton Dissociation of Solid 1,3,5-Trinitro-1,3,5-Triazinane (RDX), ChemPhysChem, 21, 837-842 (2020).   (PDF)

11.   S. K. Singh, T. Y. Tsai, B. J. Sun, A. H. H. Chang, A. M. Mebel, R. I. Kaiser, Gas Phase Identification of the Elusive N-Hydroxyoxaziridine (c-H2CON(OH)): A Chiral Molecule, J. Phys. Chem. Lett., 11, 5383-5389 (2020).   (PDF)

12.   S. K. Singh, V. Vuppuluri, S. F. Son, R. I. Kaiser, Investigating the Photochemical Decomposition of Solid 1,3,5-Trinitro-1,3,5-triazinane (RDX), J. Phys. Chem. A, 124, 6801-6823 (2020).   (PDF)

13.   S. K. Singh, J. L. Jeunesse, C. Zhu, N. F. Kleimeier, K. H. Chen, B. J. Sun, A. H. H. Chang, R. I. Kaiser, Gas Phase Identification of the Elusive Oxaziridine (cyclo-H2CONH) – An Optically Active Molecule , Chem. Commun., 56, 15643-15646 (2020).   (PDF)

14.   S. K. Singh, R. I. Kaiser, A Vacuum Ultraviolet Photoionization Study on the Isomerization, Decomposition, and Molecular Mass Growth Processes in Solid Nitromethane (CH3NO2), Chem. Phys. Lett., 766, 138343 (2021).   (PDF)