A CASSCF/CASPT2 study on the low-lying excited states of HSiCN, HSiNC and their ions

Abstract

Equilibrium geometries of low-lying electronic states of cyanosilylene (HSiCN), isocyanosilylene (HSiNC), and their ions have
been investigated using the complete active space self-consistent field (CASSCF) approach. The harmonic vibrational frequencies
on the optimized geometries were calculated using the multiconfiguration linear response (MCLR) method. Taking the further
correlation effects into account, the complete active space perturbation theory of second-order (CASPT2) was carried out for
the energetic correction. The CASPT2 calculations have been performed to obtain the vertical excitation energies of selected
low-lying excited states of HSiCN and HSiNC. Computed results show that the singlet-triplet splittings are calculated to be
0.99 and 1.30eV for HSiCN and HSiNC, respectively. The vertical excitation energies of the lowest singlet and triplet excited
states in HSiCN are lower than those in HSiNC. The first vertical ionization energy of HSiCN (10.04eV) is higher than that
of HSiNC (9.97eV). The ground-state adiabatic electron affinities are found to be rather high, and the value of HSiCN (1.85eV)
higher than that of HSiNC (1.52eV). The existences of dipole-bound excited negative ion states have been discovered within
HSiCN and HSiNC.