Are 1,5- and 1,7-dihydrodiimidazo[4,5-b:4′,5′-e]pyrazine the main products of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) alkaline hydrolysis? A DFT study of vibrational spectra

The fully optimized geometries and force fields of the most stable conformation of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane and two tautomers 1,5- and 1,7-dihydrodiimidazo[4,5-b:4′,5′-e]pyrazine were obtained at the B3LYP level of hybrid density functional theory with the 6-31G(d) basis set. The vibrational frequencies were calculated by scaling of force fields, and the vibrational spectra were interpreted taking into account potential energy distributions. DFT calculations provide good agreement between calculated and experimental vibrational frequencies, obtained for CL-20. The theoretical vibrational spectra of 1,5- and 1,7-dihydrodiimidazo[4,5-b:4′,5′-e]pyrazine correspond to the experimental FTIR spectrum obtained for the CL-20 alkaline hydrolysis products.