Electronic Structure of Neutral and Anionic Scandium Disilicon ScSi2(-/0) Clusters and the Related Anion Photoelectron Spectrum

Several quantum chemical methods including DFT (B3LYP, BP86 functional), coupled-cluster theory (RCCSD(T)), and complete active space multiconfigurational methods (CASSCF/CASPT2) were used to study the geometric and electronic structures of the scandium disilicon cluster in both neutral and anionic states, ScSi2(-/0). On the basis of the computed ground and lower-lying electronic states, and ionization energies of the anion, all the experimental bands in the anion photoelectron spectrum of ScSi2(-) can now fully be elucidated. The (3)B2 and (2)B2 states are determined to be the ground states of the anionic and the neutral triatomic species, respectively. The transition (3)B2 → (2)B2 is thus assigned to be responsible for the X band in the photoelectron spectrum. The (2)A1 neutral state is the final state corresponding to the A band. Although the first two bands arise from ionizations of scandium's 4s and 3d orbitals, all three remaining bands with higher ionization energies are the results of one-electron removals from the Si2 moiety orbitals of the anionic ground state (3)B2. Two electronic states of the same representations 1(4)B2 and 2(4)B2 are ascribed to be the carriers of the B and C bands, whereas the excited state (4)A2 is attributed to the last band D of the experimental photoelectron spectrum of ScSi2(-). From all accessible vibrations of the ground and excited states computed at the B3LYP level, a simulation of band progressions in the photoelectron spectrum was also carried out and used to provide more insights into the experimental bands.status: publishe