Abstract
The low pressure source of a Bendix time-of-flight mass spectrometer has been employed for a study of positive and negative ion formation in cyclopentadiene (C5H6). Six negative ions in the mass spectrum of C5H6 have been investigated and particular attention has been paid to the cyclopentadienyl negative ion (C5H5-). The appearance potential data for C5H5+ and C5H5- ion formation were used to estimate the following previously unknown thermochemical parameters: Δ Hf(C5H5-) = 19 ± 2 kcal mole-1, Δ Hf(C5H5) ≤ 70 ± 5 kcal mole-1, Δ Hf (C5H5+) ≤ 273 ± 4 kcal mole-1, E.A.(C5H5) ≤ 2.2 ± 0.3 eV, and D(C5H5–H) ≤ 3.9 ± 0.2 eV. A high pressure source was employed to carry out negative ion-molecule proton transfer and proton plus hydrogen transfer reactions between C5H5 and a variety of reactant ions. An evaluation of the energetics for these processes provided a second approach for the estimation of a value for Δ Hf(C5H5-) and also gave an upper limit of 58 kcal mole-1 for Δ Hf(C5H4-).
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