Abstract: The radical intermediate, which is produced in the process of electroless nickel plating, was detected in the presence of water-soluble trap α-4-pyridy1-N-tert-buty1 nitrone(POBN) or α-phenyl-tert-buty1 nitrone(PBN) by electron spin resonance(ESR) spectroscopy. The results obtained indicated that a 16-line(g=2.006 1, a^β_C—H=1.98×10^-4 T, a^γ_P—H=3.32×10^-4 T, a_N=a_P=15.93×10^-4 T) or a 18-line (g=2.004 9, a^β_C—H=a^γ_P—H=2.38×10^-4 T, a_P=17.72×10^-4 T, a_N=16.20×10^-4 T) ESR spectrum was observed in the process of electroless nickel plating when spin trap PBN or POBN was added. The spectra-line patterns and hyperfine coupling parameters were greatly indentical with those in the solution composed of Ti³⁺(0.01 mol/L)+H₂O₂(0.05 mol/L)+H₂PO₂^-(0.01 mol/L)+POBN or PBN(0.01 mol/L). Therefore, the spin adducts formed in the process of electroless nickel plating could be ascribed to the adducts belonging to HPO₂^-· and POBN or PBN and it follows that the anion radical HPO₂^-·was really produced from the oxidation of sodium hypophosphite in the process of electroless nickel plating.

Key words: Anion radical HP₂^-·, Electroless nickel plating, ESR, Spin trapping technology