Abstract: The reaction of Sc⁺ or Ti⁺ with CS₂, which was selected as a representative system of reactions of first early transition-metal ions with CS₂. The reaction mechanism of Sc⁺ or Ti⁺ in ground state and excitated state with CS₂ has been studied using the density functional theory (DFT) at B3LYP/6-311+G* level. The geometries for reactants, the transition states and the products were completely optimized. All the transition states were verified by the vibrational analysis and the intrinsic reaction coordinate (IRC) calculations. A potential energies curve-crossing diagram was investigated for state correlation between early intermediate IM1 and reactants in the reaction of Sc⁺，Ti⁺ with CS₂. The result showed that the reaction mechanism between first early transition-metal ions and CS₂ was an insertion-elimination mechanism. The main reaction path channel was detected in the reaction of Sc⁺ or Ti⁺ ground state and excitated state with CS₂.

Key words: Transition-metal ion, Carbon bisulfide, Reaction mechanism, Density functional theory