Explanation of the Colossal Sensitivity of Silicon Pentaerythritol Tetranitrate (Si-PETN)

A new extremely sensitive silicon-based explosive was recently synthesized in Germany by the nitration of tetrakis(hydroxymethyl)-silane, Si(CH$_{2}$OH)$_{4}$, with nitric acid. This sila-pentaerythritol tetranitrate (Si-PETN), Si(CH$_{2}$ONO$_{2})_{4 }$(tetrakis(nitratomethyl)-silane) has a molecular structure nearly identical to its carbon analog - PentaErythritol TetraNitrate (PETN), C(CH$_{2}$ONO$_{2})_{4}$ - with the central carbon atom replaced by silicon. Unexpectedly, SiPETN shows dramatically increased sensitivity, exploding with just a touch of a spatula, making it extremely dangerous and difficult to study. We have performed DFT calculations on paths of unimolecular decomposition and identified a novel central carbon-oxygen (or silicon-oxygen) rearrangement which shows a dramatic difference that may explain the colossal sensitivity. In particular, this reaction in SiPETN has significantly lower barrier and far more exothermic, which leads to a large net energy release at very early stages of Si-PETN decomposition facilitating a fast temperature increase and expansion of the reaction zone.