Double-proton transfer triggering mechanism of nitromethane caused by intermolecular hydrogen bonding at low temperature

Abstract

The initial triggering mechanism of nitromethane is investigated by first-principles molecular dynamics simulations and temperature-dependent Raman spectroscopy experiment. The Raman spectra at different temperature are obtained by Car-Parrinello molecular dynamics simulation to explore the activated vibration modes caused by low-temperature heat. The temperature-dependent Raman spectra experiment is constructed to compare with the theoretical data. Each possible initial reaction path caused by the activated vibration mode is analyzed to reveal the triggering mechanism of the initial chemical bond breaking for nitromethane. The results show that the intermolecular double-proton transfer is the first reaction step which is triggered by the intermolecular hydrogen bond reinforced with the active C–H stretching vibration (near 3000 cm−1), which is not reported before. The scanning energy barrier related to the increase of C–H bond lengths is about 60 kcal/mol, which is consistent with the calculated activation barrier (59.8 kcal/mol) of intermolecular proton transfer reaction. This proves the reliability of our conclusions. The results provide a new interpretation for the long-debated initial decomposition mechanism of nitromethane.

Keywords

• Energetic materials
• Raman spectra
• Active vibration modes
• Initial triggering mechanism