Potential energy nitromethane

The complete potential energy surface of nitromethane, ad-nitromethane and methyl nitrite is accurately known by experiment (Figure 7)52. Thus, the ad-nitromethane radical cation, based on appearence energy measurements, has been found as the more stable by 6 kcal mol-1. ... 

FIGURE 7. The potential energy surface of nitromethane, aci-nitromethane and methyl nitrite52. The dots indicate transitions determined from daughter ion appearance energies52. Such values may possess a significant kinetic shift3... 

Fig. 17 Potential energy diagram for the addition of nitromethane to crotonaldehyde...

Although the mechanism is far from completely determined (which is not surprising given its complexity), there are sufficient details to invite attempts to simulate the chemistry of this prototypical energetic material. Its size permits accurate ab initio calculations to determine the potential energy surface of the reactions in the proposed mechanism many of the secondary reactions are of interest in other combustion systems and have been studied by various experimental and theoretical approaches. Even a cursory discussion of the theoretical studies of secondary reactions involved in the decomposition of nitromethane is beyond the scope of this chapter we limit the discussion to the initial decomposition steps. 

In their study of the decomposition of nitromethane, Rice and Thompson [94] introduced a new approach for constructing potential energy surfaces for many-atoms systems that react via multiple pathways. The basic idea of the approach is to construct potentials that accurately describe the various equilibrium regions, e.g., reactants and products, and then write the overall global potential as Vtotal=E SjV where j denotes the various stable species, the Vi are the analytical potentials for those species, and the Sj are weighting functions that effect a switching between the potentials... 

ELECTRON AFFINITIES AND POTENTIAL ENERGY CURVES FOR NITROBENZENE AND NITROMETHANE... 

ABSTRACT Work has begun at RARDE to attempt to elucidate the complex chemistry of reacting explosives using molecular orbital calculations to describe possible potential energy surfaces for decomposition. The well-known sensitising effect of amines on nitromethane is modelled by studies of the nitromethane/ammonia system. The calculations lead to a new proposal for a mechanism for decomposition. This mechanism is supported by experimental data. 

TABLE 15. Ionization nitromethane potentials IP (eV) and orbital energies (eV) of... 

More accurate quantum chemistry methods for large molecules have become feasible since the Rice and Thompson [94] analytical potential was developed. The capabilities were illustrated by Manaa and Fried [98] in a DFT and ab initio study of the C-N bond dissociation energy for the singlet and triplet states of nitromethane. 

Due to its success describing both the solid and liquid phases of nitromethane as well as its reliability and transferability for a large number of important energetic materials, Sorescu et al. [137] indicated that this set of potentials can be further extended to investigate the energy transfer, the solid-liquid phase transitions, or different reactions in condensed phase. 

The resulting radical, CH2 N02, then adds to another molecule of nitromethane. It was concluded that the reaction path depends not only on the oxidation potentials but also on the energy of the bond formed during addition. 

Fewer than 300 Ea for organic molecules have been determined in the gas phase. The majority of the Ea have been determined by the ECD and/or TCT methods. The direct capture magnetron, AMB, photon, and collisional ionization methods have produced fewer than 40 values. Only the Ea of p-benzoquinone, nitrobenzene, nitromethane, azulene, tetracene, and perylene have been determined by three or more methods. Excited-state Ea have been obtained by each of these methods. Half-wave reduction potentials have determined the electron affinities of 50 aromatic hydrocarbons. The electron affinities of another 50 organic compounds have been determined from half-wave reduction potentials and the energies of charge transfer complexes. It is a manageable task to evaluate these 300 to 400 Ea. 

Aside from the sensitizers described above, nitrate and ammonium nitrate can also be employed as explosive sensitizer for nitromethane. In addition, adding metal powder (e.g., A1 powder) into nitromethane can increase the corresponding explosion energy and detonation sensitivity. To prevent potential separation of solid components, nitrocellulose or cellulose acetate may be used as thickener [40, 41]. 

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