Abstract: The molecular structure, atomization energy, ionization energy, electron affinity and vibrational spectra of silicon dihalides, SiX2 (X = F, Cl, Br, I), have been obtained using theoretical methods in the gas phase. The neutral dihalides, their cations and anions have been studied in C2v symmetry. The neutral species have been considered in both the 1A1 singlet and 3B1 triplet states whereas the cations (SiX2+) and anions (SiX2−) have been considered in the 2A1 and 2B1 states, respectively. The methods used are Møller-Plesset perturbation theory (MP2), density functional theory (DFT), Gaussian-2 (G2) and complete basis set methods (CBS-4 and CBS-Q). The functional used for the DFT method is B3LYP. The basis sets used are 6-311++G(d,p) for all atoms except that 6-311G(d,p) has been used for iodine atom only. The silicon dihalides, their cations and anions have been fully optimized using MP2 and DFT methods. Single point energy computations (G2, CBS-4M and CBS-Q) have been performed except for silicon diiodide. The results obtained are in good agreement with literature although they are method dependent.
