Hydrocarbon Energetics

Methane was one of the first molecules used to illustrate the effectiveness of fixed-node DQMC calculations relative to standard ab initio methods. The first fixed-node DQMC calculations for methane recovered 97% of the correlation energy and gave a total electronic energy 30 kcal/mol below the lowest energy variational result (at the time) and only 3 kcal/mol above the experimental value. Since then many more calculations for a large variety of carbon and hydrocarbon systems have shown similarly impressive results. These systems ranged from methylene to graphite and diamond structures and were treated with and without pseudopotentials. 

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To make an IE the oxidizer must be combined with a suitable fuel. The majority of fuels available for use in IEs are hydrocarbons (materials containing mostly carbon and hydrogen). These materials are often referred to as organic compounds due to their prevalence in living organisms. Potential fuels can be broken down into three categories hydrocarbons, energetic hydrocarbons, and elementals. ... 

For intermediate temperatures from 400-1000°C (Fig. 11), the volatilization of carbon atoms by energetic plasma ions becomes important. As seen in the upper curve of Fig. 11, helium does not have a chemical erosion component of its sputter yield. In currently operating machines the two major contributors to chemical erosion are the ions of hydrogen and oxygen. The typical chemical species which evolve from the surface, as measured by residual gas analysis [37] and optical emission [38], are hydrocarbons, carbon monoxide, and carbon dioxide. 

Methane is unique among hydrocarbons in being thermodynamically stable with respect to its elements. It follows that pyrolytic reactions to convert it to other hydrocarbons are energetically unfavourable and will be strongly equilibrium-limited. This is in marked contrast to the boranes where mild thermolysis of B2H6 or B4H10, for example, readily yields mixtures of the higher boranes (p. 164). Vast natural reserves of CH4 gas exist but much is wasted... 

Hydrazinium diperchlorate (HP2) is one of the higher energetic oxidizers considered for use in composite solid propints with hydrocarbon binders. Its other advantages include high density, high burning rate, and moderate projected cost. Its shortcomings include relatively poor stability to vibrational and thermal shock... 

A theoretical explanation for such an anomalous phenomenon in certain nonalternant hydrocarbons has first been attempted, in case of pentalene, by Boer-Veenendaal and Boer followed by Boer-Veenen-daal et Snyder and Nakajima and Katagiri for other related nonalternant hydrocarbons. By making allowance for the effects of <7-bond compression, these authors have shown that a distorted structure resembling either of the two Kekule-type structures is actually energetically favored as compared with the apparently-full symmetrical one. 

Measuring enthalpy changes for the dissolution of hydrocarbons, such as alkanes, in water shows that heat is evolved, i.e., A/f is negative and energetically water and alkanes attract each other. However, such attraction does not make alkanes soluble in water to any appreciable extent. This is because the free energy change AGsomtion opposes the process and is positive. 

Polar compounds and compounds that ionize can dissolve readily in water. These compounds are said to be hydrophilic. In contrast to hydrophilic substances, hydrocarbons and other nonpolar substances have very low solubility in water because it is energetically more favorable for water molecules to interact with other water molecules rather than with nonpolar molecules. As a result, water molecules tend to exclude nonpolar substances, forcing them to associate with themselves in forming drops, thereby minimizing the contact area between... 

The reaction 0(3P) + C2H2 plays a key role not only in the combustion of acetylene itself,53 but also in the overall mechanism for hydrocarbon combustion, since acetylene is an important intermediate in the combustion of methane, larger aliphatic hydrocarbons, and aromatics.54-57 There are two energetically-allowed channels ... 

The fact that quadricyclene and dienes quench the fluorescence of aromatic hydrocarbons despite the fact that the energetics for classical energy transfer are very unfavorable has been rationalized by the formation of an exciplex. A general mechanism is as follows ... 

A mechamism closely related to that of (29) can be viewed for the loss of methyl radicals from terminal positions of ionized n-alkanes54. For example, based on experiments with 2H-labelled hydrocarbons and on careful analysis of energetic data it was shown convicingly that CD3 loss from 128 gives only the secondary cation 130. From the fact that 131 is not found to be formed at all, it must be concluded... 

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