A CASSCF/CASPT2 investigation on electron detachments from ScSi _n^- (n = 4-6) clusters

In this work, the low-lying states of several isomers of ScSi _n^-/0 (n = 4-6) were investigated with the B3LYP functional and CASPT2 method. The ground states of the anionic clusters were predicted to be the singlet states of the trigonal bipyramid ScSi₄^- (A-ScSi₄^-), the face-capped trigonal bipyramid ScSi₅^- (A-ScSi₅^-), and the pentagonal bipyramid ScSi₆^- (A-ScSi₆^-) isomer. Based on the anionic ground states, all the relevant electron detachment processes were identified. The corresponding adiabatic and vertical detachment energies (ADEs and VDEs) of the anionic clusters were computed at the CASPT2 level. The calculated results were used to interpret all the important features in the photoelectron spectra of ScSi _n^- (n = 4-6) clusters. Franck-Condon factor simulations were also performed based on the B3LYP geometries, vibrational frequencies, and normal modes to explain the shapes of the first bands in the spectra.