title: Experimental and theoretical studies of the decomposition of new imidazole based energetic materials: model systems.
abstract: 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 S(2) nitroimidazole molecules relax to the S(1) state through the (S(2)∕S(1))(CI) conical intersection, and undergo a nitro-nitrite isomerization to generate the NO product from the S(1) potential energy surface. Nevertheless, NO(2) elimination and nitro-nitrite isomerization are expected to be competitive reaction mechanisms for the decomposition of these molecules on the ground state potential energy surface from the Franck-Condon equilibrium geometry through thermal dissociation.
authors.affiliation: Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Zijun
authors.initials: Z
authors.lastname: Yu
authors.forename: Elliot R
authors.initials: ER
authors.lastname: Bernstein
mesh_terms: D007093:Imidazoles / Q000737:chemistry*; D015394:Molecular Structure; D009569:Nitric Oxide / Q000737:chemistry; D009585:Nitrogen Dioxide / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D007093:Imidazoles; D009569:Nitric Oxide; D009585:Nitrogen Dioxide