Calculation of the ECD and NIMS Temperature Dependence

For the compounds with electron affinities less than 1.5 eV, such as the chlorinated dibenzodioxins, benzofurans, biphenyls, and naphthalenes, the temperature dependence of the ECD will be important but has not been measured. With estimates of the electron affinities, kinetic parameters, and bond dissociation energies, temperature dependence can be predicted from the kinetic model. This is illustrated for the chlorinated naphthalenes and biphenyls. These calculations may suggest the best conditions for analysis. 

The electron affinities of halogenated aromatic and aliphatic compounds and nitro compounds have been evaluated. Additional electron affinities for halogenated benzene, freons, heterocyclic compounds, dibenzofuran, and the chloro- and fluoroben-zenes are reported from ECD data. The first positive Ea for the fluorochloroethanes were obtained from published ECD data. The Ea of halogenated aromatic radicals have been estimated from NIMS data. The AEa of all the halobenzenes have been calculated using CURES-EC. The Ea of chlorinated biphenyls and chlorinated napthalenes obtained from reduction potentials have been revised based on variable solution energy differences. 

The TCT Ea of perfluoromethylcyclohexane is confirmed with NIMS data and the Ea of perfluoromethylcyclopentane is reported. The EDEA for the loss of the tertiary fluorine atom is determined for both these compounds. In many cases the NIST values for fluorinated hydrocarbons could be for excited states. In all but a few of the cases, there is only one experimental determination of the Ea so confirmation using the CURES-EC procedure is important. 

The activation energies for dissociative thermal electron reactions have been correlated with bond dissociation energies when available. Estimates of activation energies for dissociative reactions have been made by assuming a fixed value for A i and using relative molar responses or relative rate constants to calculate activation energy differences. Additional bond dissociation energies are obtained from these data. 

The temperature dependence of negative-ion mass spectra of environmental compounds has been analyzed in terms of the electron affinities and EDEA values. Morse potential energy curves have been constructed using the Herschbach parameters to illustrate the different types of thermal electron reactions. The temperature dependence of the ECD response for chlorinated naphthalenes and biphenyls has been predicted and is compared with experimental data for several pesticides and chlorinated biphenyls. 

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