Experimental and theoretical studies of the decomposition of new imidazole based energetic materials: Model systems

Decomposition of three imidazole based model energetic systems (2-nitroimidazole, 4-nitroimidazole, and 1-methyl-5-nitroimidazole) is investigated both experimentally and theoretically. The initial decomposition mechanism for these three nitroimidazoles is explored with nanosecond energy resolved spectroscopy, and quantum chemical theory at the complete active space self-consistent field (CASSCF) level. The NO molecule is observed as an initial decomposition product from these three nitroimidazoles subsequent to UV excitation. A unique, excitation wavelength independent dissociation channel is observed for these three nitroimidazoles that generates the NO product with a rotationally cold (∼50 K) and a vibrationally mildly hot (∼800 K) distribution. Potential energy surface calculations at the CASSCF/6-31G(d) level of theory illustrate that conical intersections play an important and essential role in the decomposition mechanism. Electronically excited S2 nitroimidazole molecules relax to the S1 state thro...