Large carbon cluster anions generated by laser ablation of graphene

The formation of large even-numbered carbon cluster anions, C(n)⁻, with n up to 500 were observed in the mass spectra generated by laser ablation of graphene and graphene oxide, and the signal intensity of the latter is much weaker than that of the former. The cluster distributions generated from graphene can be readily altered by changing the laser energy and the accumulation period in the FT-ICR cell. By choosing suitable experimental conditions, weak signals of odd-numbered anions from C₁₂₅⁻ to C₂₁₁⁻, doubly charged anions from C₇₀²⁻ to C₂₃₀²⁻ and triply charged cluster anions from C₈₀³⁻ to C₂₂₄³⁻ can be observed. Tandem MS was applied to some selected cluster anions. Though no fragment anions larger than C₂₀⁻ can be observed by the process of collisional activation with N(2) gas for most cluster ions, several cluster anions can lose units of C(2), C(4), C(6) or C(8) in their collision process. The differences in their dissociation kinetics and structures require further calculations and experimental studies.