Unimolecular reaction dynamics of dimethylnitramine

The unimolecular reaction dynamics of dimethylnitramine are studied using classical trajectories on three model potential-energy surfaces. Elimination of NO₂ is the predominant reaction. The focus of this study is on the simple, bond-rupture reaction to give NO₂. Rate constants are calculated for two of the potentials at two different energies and individual trajectories are examined to determined the nature of the energy flow in the molecule prior to reaction and the product energy distribution. Energy flow into the nitro group increases significantly prior to reaction. Energy becomes trapped in the nitro group as the N-N bond begins to break and rapidly exchanges between the NO₂ bending and stretching modes. One of the potentials allows the concerted molecular elimination of HONO. The concerted process which involves hydrogen migration and subsequent HONO elimination accounts for less than 5% of the reactive trajectories. However, the HONO elimination reaction can be enhanced by exciting high CH stretch overtones.