## 3 Results and Discussion
### Pristine Fullerite C\({}_{60}\) Study
It was also found [51] that the BE of C 1s electron in crystalline fullerite is 0.4 eV less than in the gas-phase C\({}_{60}\) molecule. It should also be emphasized that the shape and energy positions of absorption bands in the C 1s NEXAFS spectra of crystalline and molecular C\({}_{60}\) coincide. This is evidence for a negligible effect of neighboring molecules on the C 1s NEXAFS spectrum due to the weakness of intermolecular interactions. Therefore, the calculation data for the C\({}_{60}\) cluster can be used to interpret the C 1s NEXAFS spectrum of fullerite [34]. The icosahedral-symmetric C\({}_{60}\) theoretical study [34] shows the expediency of extending the Huckel molecular orbital method, previously used for planar conjugate systems (where each carbon atom forms three two-electron localized \(\sigma\)-bonds with neighboring atoms, and the fourth electron is located on the \(\pi\)-orbital orthogonal to the three \(\sigma\)-orbitals), to large spheroidal molecules. The C\({}_{60}\) molecular structure has the non-planar (pyramidal) atom arrangement. This affects the \(\pi\)-orbital nature and leads to the presence of frame stresses and decreases the fullerene thermodynamic stability compared to graphite [52]. It should be noted that the \(\pi\)- and \(\sigma\)-orbital approximation for the C\({}_{60}\) molecule is not strict. However, for large surfaces, the \(\pi\)-like orbitals are oriented close to the normal to the surface, and \(\sigma\)-like--tangential to the surface. In the literature, there are extensive data on the nature of the C 1s NEXAFS spectrum of the C\({}_{60}\) fullerene molecule, theoretically calculated in various approximations [34; 52; 53; 54]. On their basis peaks 1-4 (Figure 1d) can be identified as a result of C 1s electron transitions to the unoccupied molecular orbitals (MO) of t\({}_{\rm 1u}\), t\({}_{\rm 1g}\), h\({}_{\rm g}\) and t\({}_{\rm 2u}\) symmetry, respectively. The structures 5-11 above the C 1s ionization threshold are not unambiguously identified at present. However, the band structure calculations for the fullerite C\({}_{60}\) with an fcc lattice within the density functional theory [55] showed that the \(\pi\)-zones are located in the range of BE from \(-6\) eV to +7 eV, and the bonding and antibonding \(\sigma\)-states are located lower and higher on the energy scale, respectively. Thus, sharp peaks 5-8 can be attributed to C 1s electron transitions to the \(\pi^{\circ}\) MOs, and broad bands 9-11 to those to \(\sigma^{\circ}\) MOs. The vertical dashed lines in Figure 1d indicate the positions of the peaks corresponding to C 1s \(\rightarrow\)\(\pi^{\circ}\) transitions in the atomic groups C=O (288.9 eV), C\(-\)O\(-\)C (287.2 eV) and C\(-\)O (286.7 eV) [43]. The Figure 1d clearly shows the absence of such features in the C 1s NEXAFS spectra of the C\({}_{60}\) and HOPG. This indicates that the above O 1s XPS peaks are related to oxygen and water molecules physically adsorbed on the surfaces of C\({}_{60}\) and HOPG without the formation of an oxygen-carbon chemical bond. Numerous studies of the adsorption of oxygen compounds on the surfaces of C\({}_{60}\) fullerite powder and films [56; 57; 58; 59; 60] showed that at temperatures below 470 K water molecules from the air are physically adsorbed and remain on the surface even under high vacuum conditions. Since in our experiments, investigation was carried out at room temperature, most likely, there was a physical adsorption of water molecules. It was shown that when the samples are heated in a vacuum, some of the water molecules remain on the sample surface up to a temperature above 570 K, carbon oxides begin to form [35]. The XPS study of fullerite C\({}_{60}\)[58; 60] showed that the BE of O 1s electrons of water molecules adsorbed on the fullerite surface is in the 532-534 eV energy range and significantly less than that in a free H\({}_{2}\)O molecule (535.75 eV) [61].