Formation of astrochemically relevant molecular ions: Reaction of translationally coldCCl+with benzene in a linear ion trap

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The gas-phase ion-neutral reaction of ${\mathrm{CCl}}^{+}$ $+$ benzene $({\mathrm{C}}_{6}{\mathrm{H}}_{6})$ is investigated using a linear Paul ion trap coupled to a time-of-flight mass spectrometer. Low collision energies are achieved by sympathetically cooling ${\mathrm{CCl}}^{+}$ reactant ions with cotrapped laser-cooled ${\mathrm{Ca}}^{+}$. The observed products include the astrochemically relevant carbocations ${\mathrm{C}}_{7}{\mathrm{H}}_{5}^{+}$, ${\mathrm{C}}_{5}{\mathrm{H}}_{3}^{+}$, and ${\mathrm{C}}_{3}{\mathrm{H}}_{3}^{+}$, as well as ${\mathrm{C}}_{3}{\mathrm{H}}_{2}{\mathrm{Cl}}^{+}$. Branching ratios of these products are measured, and ${\mathrm{C}}_{7}{\mathrm{H}}_{5}^{+}$, a carbon-growth species, is favored. Complementary electronic structure calculations provide thermodynamic limits for the reaction and allow for assignment of reaction products to specific structural isomers. Only one exoergic isomer is identified for each observed product with the exception of ${\mathrm{C}}_{7}{\mathrm{H}}_{5}^{+}$ where many identified structural isomers are exoergic. The results from this Letter broaden our understanding of the reactivity and possible role of ${\mathrm{CCl}}^{+}$ and ${\mathrm{C}}_{6}{\mathrm{H}}_{6}$ in interstellar chemistry. Furthermore, this Letter provides insight into a potential pathway to larger carbocations that may be precursors to more complex polycyclic aromatic hydrocarbons.