Stability of neutral molecular polynitrogens: energy content and decomposition mechanisms

The potential application of all-nitrogen molecules as high energy density materials (HEDMs) has been attracting considerable scientific effort. If stable enough to be synthesized and stored, these systems may be used as a green source of energy. However, it is very difficult to obtain these structures under mild experimental conditions. Theoretical chemistry may aid in the search for polynitrogens that are more likely to have experimental usability. The barriers towards decomposition are an effective way to assess their stability, but these have not been thoroughly studied. Most of the previous effort in this direction focus on a single N case, each employing different accuracy levels, and the decomposition of caged structures has been little explored. Here we explore the stability and decomposition of several neutral molecular polynitrogens of different sizes and shapes using a common and accurate theoretical framework in order to compare among them, search for patterns and identify potential candidates for synthesis. We focus especially on new caged geometries, and our results indicate that the prismatic ones can be expected to present higher energy densities and be very stable with respect to unimolecular decomposition. It is shown that the energy content can be clearly stratified between chain, ring, cage and prismatic cage structures.