Ab Initio Molecular Orbital Study of the Electron Emission Mechanism of TiCl₃ as a Reductant for an Electroless Deposition Process

Abstract

The oxidation mechanism of TiCl₃ as a reductant for an electroless deposition process was studied by ab initio molecular orbital method. The reaction process of TiCl₃ proceeds with the substitution of Cl⁻ to OH⁻. Net charge and spin density of the reactant, product, and intermediates were evaluated. It was suggested that the electron emission of TiCl₃, which is originated by the oxidation of Ti(III) to Ti(IV), took place when Cl is replaced by OH⁻ to form Ti(OH)₄. The catalytic activity of the metal surface, which is one of the most important factors for the electroless deposition process, was studied using a Pd₄ cluster as a model surface. It was suggested that the Pd₄ cluster enhanced the reaction of TiCl₃ to emit the electron. The effect of solvation is also taken into account in terms of the dielectric field constant. It was indicated that the heat of oxidation reaction shifted to an exothermic reaction with decreasing dielectric constant, indicating that the reaction preferentially proceeds in the vicinity of solid/liquid interface. However, it was indicated that the reaction could proceed in the bulk solution, suggesting that appropriate stabilization such as formation of complex is required for the application of the TiCl₃ to the electroless deposition process.