The X-ray spectra have good isomer dependence and give a comprehensive insight of the electronic structure of the system.

X-ray photoelectron spectra (XPS), near-edge X-ray absorption fine structure spectra (NEXAFS), and X-ray emission spectroscopy (XES), as well as the ground-state electronic/geometrical structures about the significant classical isolated-pentagon rule (IPR) isomer D 3h -#24109C78, the non-IPR isomers C 2-#22010C78 and C 1-#23863C78, and the nonclassical isomer C 2-C78(NC2) with its chlorinated derivative C 2-C78(NC2)­Cl24, which are newly obtained in the experiment, have been calculated at the density functional theory (DFT) level. Significant differences have been observed in the electronic structure and the X-ray spectra. All X-ray spectra have shown strong isomer dependence; consequently, the “fingerprint” in X-ray spectra shows a very effective way to isolate the fullerene isomers above. As a result, this work indicates that X-ray spectroscopy can provide valuable identification for classical and nonclassical fullerenes as well as their derivatives on experimental and theoretical studies.

X-ray photoelectron and near-edge X-ray absorption fine structure (NEXAFS) spectra, as well as the ground-state electronic/geometrical structures of a newly discovered nonclassical isomer C 2v -C66(NC), and two classical fullerene isomers C 2-#4466C66 and C s -#4169C66 with their hydrogenated derivatives [C 2v -C66H4(NC), C 2-#4466C66H4, and C s -#4169C66H4] have been calculated at the density functional theory (DFT) level. Significant differences were observed in the electronic structures and simulated X-ray spectra after hydrogenation. Simultaneously, both X-ray photoelectron and NEXAFS spectra reflected conspicuous isomer dependence, indicating that the “fingerprints” in the X-ray spectra can offer an effective method for identifying the above-mentioned fullerene isomers. The simulated ultraviolet–visible (UV–vis) absorption spectroscopy of C 2v -C66H4(NC) has also been generated by means of the time-dependent DFT method, and the calculations are well consistent with the experimental results. Consequently, this work reveals that X-ray and UV–vis spectroscopy techniques can provide valuable information to help researchers explore the fullerene electronic structure and isomer identification on the future experimental and theoretical fullerene domains.