Abstract: Using density functional theory(DFT),the geometries and the vibrational frequencies of linear cluster SC2nS2－(n=1～12) have been investigated at the B3LYP/6-31G* level. Time-dependent density functional theory(TD-DFT) has been used to calculate the vertical transition energies and oscillator strengths for transitions of SC2nS2－ at the B3LYP/cc-pvTZ and B3LYP/cc-pvDZ levels. On the basis of theoretical results, an explicit expression for the size dependence of the excitation energy in linear carbon chains is obtained. Present calculations show that the terminal sulfur atom may significantly affect the excited-state properties of the conjugated carbon chains. At the B3LYP/ 6-311＋G*level, the single-point energies of the ionic clusters have been calculated in order to determine the first ionization energies. The relationship between the cluster size and the first ionization energies of the linear carbon chains is proposed.

Key words: SC2nS2－, DFT, TD-DFT, Electronic spectra, Ionization energies, 　Analytic expression