Energies of Electronic Transitions of Pentaerythritol Tetranitrate Molecules and Crystals

Abstract

Despite significant effort in research on energetic nitrocompounds coupled with a great interest in these materials for a range of technological and medical applications, the electronic structure of condensed energetic materials is barely studied. In this research aimed at a better understanding of the low energy absorption in the optical spectrum of nitro-compounds, the electronic structure and vertical electronic transitions of a gas-phase pentaerythritol tetranitrate (PETN) molecule and an ideal PETN crystal were explored by means of density functional theory based calculations. In accordance with most experimental observations, the optical absorption spectrum of PETN has a well-resolved intense band above 6 eV that is accompanied by a few low intensity broad bands at lower energies. Our modeling suggests that the high intensity band corresponds to a series of strong singlet−singlet transitions, while the lower energy bands are attributed to the formation of tightly bound singlet and triplet excitons. All transitions are well-localized on O−NO 2 groups of PETN. We also systematically analyze low energy excitations in other nitro-compounds, which exhibit similar patterns in the spectra even though the experimental data are incomplete at the moment. We predict that tightly bound excitons and charge transfer excitons should exist in PETN and both would trigger the nitrate decomposition, which allows for precise control of the initiation process.

Photochemistry of the α-Al2O3-PETN Interface

“…The optical absorption of PETN molecules and crystals were recently studied in great detail [23]. The UV absorption spectrum of PETN consists of three broad bands: a strong electronic transition at or below 193.5 nm (>6.41 eV) [37,38,39] and two weak transitions at 260 nm (4.77 eV) [37,38] and 290 nm (4.27 eV) [37].…”

“…Our current research was inspired by an idea of achieving a highly controllable explosive decomposition chemistry initiated by photo-excitation with standard available lasers. In a series of recent experiments [18,19,20,21] and quantum-chemical simulations [22,23], it was fundamentally established that the decomposition of a high explosive material, PETN, can be reliably triggered by laser irradiation once PETN crystals are mixed with a small fraction of micron size metal oxide (e.g., MgO) powders. This demonstrated that there is a strong dependence of the initiation process on the presence of the oxide.…”

“…However, once they form an interface, or a composite, their optical, electronic, and photochemical properties significantly change. Thus, oxygen vacancies at the MgO surface facilitate strong chemical adsorption of PETN on MgO, induce a charge transfer, and consequently may initiate the PETN decomposition by laser light with the photon energy of 1.17 eV, with an unusually low activation barrier [22,23].…”

Relaxed structure of typical nitro explosives in the excited state: Observation, implication and application

“…4, which is different from that of RDX 0 . -HMX 0 , CL-20 0 and PETN 0 have a similar structures to RDX 0 [7,[9][10][11]35,37]. The detailed relaxation processes are given in supplementary information.…”

“…The photo-excitation process (process 1) is a widely studied process, and the excitation energy is clearly seen in the steady optical absorption spectra [34,36,37]. The nitro group exhibits special behavior owing to a large conjugated NO 2 π* orbital [10,15,16,18,19,30], which has been shown to be an energy pitfall for nitro explosives [15,16,[18][19][20].…”