Thermal energy electron detachment rate constants. The electron detachment from azulene− and the electron affinity of azulene

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Abstract
The rate constant kd and its temperature dependence for thermal electron detachment from the azulene negative ion Az−⇄ad Az+e was determined by observing, at suitably high temperature, the decay of Az− with time. A pulsed electron beam, high ion source pressure mass spectrometer was used. The reaction mixtures typically contained 4 Torr CH4 as bath gas and azulene and perfluoromethylcyclohexane (C7F14) at pressures of a few mTorr. The C7F14 which has a large electron attachment coefficient was used as electron scavenger in order to suppress the (re)attachment of electrons to Az. The experimental data points for kd could be fitted equally well with the expressions kd =2.5×106 T3/2 (s−1)exp[−14.5 (kcal/mol)/RT] and kd =1.14×1011 (s−1)exp[−15.7 (kcal/mol)/RT]. The activation energies are close to the electron affinity E.A.(Az)=16 kcal/mol obtained in earlier determination from this laboratory. Consistent values for the equilibrium constant K of the attachment–detachment equilibrium can be obtained when K is evaluated from E.A.(Az) and third law entropies of the reactants and from K=ka/kd, where ka and kd are experimentally determined quantities. The ka values were taken from Christophorou.