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 through the (S2/S1)CI conical intersection, and undergo a nitro-nitrite isomerization to generate the NO product from the S1 potential energy surface. Nevertheless, NO2 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.
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See supplementary material at http://dx.doi.org/10.1063/1.4752654 for details of calculations and methods.
© 2012 American Institute of Physics.
2012
American Institute of Physics
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