Laboratory study of the formation of fullerene (from smaller to larger, C44 to C70)/anthracene cluster cations in the gas phase

Abstract

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 (C14H10). 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., (C14H10)C(60 – 2n) +, n = 1 – 8 and (C14H10)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.