From lattice vibrations to molecular dissociation

In this chapter, we explore the mechanochemical principles that underpin the initiation of energetic molecular crystals by mechanical impact, and outline recent developments to the vibrational up-pumping model to predict the impact sensitivities for a structurally and energetically diverse set of molecular crystals. The model is based on impact energy adsorption by the lattice acoustic modes, resulting in heightened phonon scattering through a two-stage up-pumping process, as defined within the first-order anharmonic approximation limit. Efficient trapping of the up-pumped vibrational energy into the molecular vibrations indicates an impact-sensitive energetic molecular crystal. The structural distortions that result induce changes in the crystal electronic structure such as band gap narrowing, which in turn facilitates excitation of electrons and formation of unstable species on the time scales of molecular vibrations. The vibrational up-pumping model therefore provides a predictive tool to rationalize the impact sensitivity response of energetic molecular crystals, from lattice vibration excitation through to molecular dissociation and initiation.