On the Release of Stored Energy from Energetic Materials

Grinding, shocking, rapidly crushing, or electrically stimulating organic solids generates a variety of excited electronic state species including atoms, ions, radicals, fragments, etc., that are reactive on an ultrafast (<100 fs) timescale. In this review, we present the nonadiabatic theory that describes such species kinetics and dynamics that initiate, drive, and sustain the decomposition of energetic materials. The quantum mechanical theory that models this behavior is discussed in detail with regard to the excitation of energetic and nonenergetic model systems. The multireference approach taken can distinguish similar energetic and nonenergetic molecules with respect to their decomposition behavior and generation of an initial product fragment. The theory described involves complete active space self-consistent field calculations of adiabatic potential energy surfaces that interact nonadiabatically at conical intersections (Os). The CIs are thereby responsible for the ultrafast kinetics and dynamics that generate the initial fragmentation behavior of both energetic and nonenergetic molecules. This energy release mechanism has two important consequences for the decomposition of the Molecular species of interest: (1) the molecule is excited to higher electronic states and thereby has of the order of at least 5 eV of energy to break bonds; and (2) through various CIs the energetic molecule can return to the ground electronic state (in <100 fs) at a very different part of its ground state potential energy surface so that unexpected new reactive radicals can be generated. We demonstrate such behavior for energetic and nonenergetic nitramines, furazans, tetrazines, imidazoles, and other energetic systems. Our approach readily distinguishes energetic from nonenergetic molecular behavior both theoretically and experimentally.