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Dissociation of the Anthracene Radical Cation: A Comparative Look at iPEPICO and Collision-Induced Dissociation Mass Spectrometry Results
The dissociation of the anthracene
radical cation has been studied
using two different methods: imaging photoelectron photoion coincidence
spectrometry (iPEPCO) and atmospheric pressure chemical ionization–collision
induced dissociation mass spectrometry (APCI-CID). Four reactions
were investigated: (R1) C<sub>14</sub>H<sub>10</sub><sup>+•</sup> → C<sub>14</sub>H<sub>9</sub><sup>+</sup> + H, (R2) C<sub>14</sub>H<sub>9</sub><sup>+</sup> → C<sub>14</sub>H<sub>8</sub><sup>+•</sup> + H, (R3) C<sub>14</sub>H<sub>10</sub><sup>+•</sup> → C<sub>12</sub>H<sub>8</sub><sup>+•</sup> + C<sub>2</sub>H<sub>2</sub> and (R4) C<sub>14</sub>H<sub>10</sub><sup>+•</sup> → C<sub>10</sub>H<sub>8</sub><sup>+•</sup> + C<sub>4</sub>H<sub>2</sub>. An attempt was made to assign structures to
each fragment ion, and although there is still room for debate whether
for the C<sub>12</sub>H<sub>8</sub><sup>+•</sup> fragment ion
is a cyclobutaÂ[<i>b</i>]Ânaphthalene or a biphenylene cation,
our modeling results and calculations appear to suggest the more likely
structure is cyclobutaÂ[<i>b</i>]Ânaphthalene. The results
from the iPEPICO fitting of the dissociation of ionized anthracene
are <i>E</i><sub>0</sub> = 4.28 ± 0.30 eV (R1), 2.71
± 0.20 eV (R2), and 4.20 ± 0.30 eV (average of reaction
R3) whereas the Δ<sup>‡</sup><i>S</i> values
(in J K<sup>–1</sup> mol<sup>–1</sup>) are 12 ±
15 (R1), 0 ± 15 (R2), and either 7 ± 10 (using cyclobutaÂ[<i>b</i>]Ânaphthalene ion fragment in reaction R3) or 22 ±
10 (using the biphenylene ion fragment in reaction R3). Modeling of
the APCI-CID breakdown diagrams required an estimate of the postcollision
internal energy distribution, which was arbitrarily assumed to correspond
to a Boltzmann distribution in this study. One goal of this work was
to determine if this assumption yields satisfactory energetics in
agreement with the more constrained and theoretically vetted iPEPICO
results. In the end, it did, with the APCI-CID results being similar