2020RAA....20..202Z

The formation and evolution mechanism of fullerenes in the planetary nebula or in the interstellar medium are still not understood. Here, we present the study on the cluster formation and the relative reactivity of fullerene cations (from smaller to larger, C₄₄ to C₇₀ ) with anthracene molecule (C₁₄ H₁₀). The experiment is performed in an apparatus that combines a quadrupole ion trap with a time-of-flight mass spectrometer. By using a 355 nm laser beam to irradiate the trapped fullerenes cations (C₆₀⁺ or C₇₀⁺ ), smaller fullerene cations C_(60–2n)⁺ , n = 1-8 or C_(70–2m)⁺ , m = 1-11 are generated, respectively. Then reacting with anthracene molecules, series of fullerene/anthracene cluster cations are newly formed (e.g., (C₁₄ H₁₀)C_(60–2n)⁺ , n = 1-8 and (C₁₄ H₁₀)C _(70-2m) _⁺ , m = 1-11), and slight difference of the reactivity within the smaller fullerene cations are observed. Nevertheless, smaller fullerenes show obviously higher reactivity when comparing to fullerene C₆₀⁺ and C₇₀⁺ . A successive loss of C₂ fragments mechanism is suggested to account for the formation of smaller fullerene cations, which then undergo addition reaction with anthracene molecules to form the fullerene-anthracene cluster cations. It is found that the higher laser energy and longer irradiation time are key factors that affect the formation of smaller fullerene cations. This may indicate that in the strong radiation field environment (such as photon-dominated regions) in space, fullerenes are expected to follow the top-down evolution route, and then form small grain dust (e.g., clusters) through collision reaction with co-existing molecules, here, smaller PAHs.