Kinetic stability and reactivity of silicon and fluorine-containing CL-20 derivatives
CL-20 based cages in which carbon/oxygen atoms are replaced by silicon/fluorine ones are studied using the ab initio molecular dynamics, density functional theory, and time-dependent density functional theory. In contrast to the pristine CL-20, the first step of pyrolysis of these cages is the migration of oxygen/fluorine atoms to silicon. Molecules containing fluorine are unstable at room temperature. The high-energy silicon-containing molecule (CSi5H6N12O12) is approximately as stable as pristine CL-20. Energy barrier preventing its decomposition is about 200 kJ/mol. Energies of the frontier orbitals and reactivity descriptors of CSi5H6N12O12 are very close to the corresponding values of pure CL-20. All studied cages can form covalent dimers via the methylene molecular bridges. It is found that the reactions of dimerization are exothermic. Dimers’ isomers in which silicon atoms are located closer to the methylene bridges possess lower internal energies. It is found that the mechanisms of dimers’ thermal decomposition are similar to the analog mechanisms of corresponding monomers. Dimerization of the cages results in the redshifts of their ultraviolet spectra.
Keywords ---hexanitrohexaazaisowurtzitane, HNIW, pyrolysis mechanism, ab initio molecular dynamics, transition state, dimers