Pulse radiolytically generated (SCN)(2)(.-) radicals bind strongly to the gold nanoparticle surface, with an apparent equilibrium constant of 4.7 x 10(3) M-1. The resultant complex has a strong absorption band at 390 nm which quickly undergoes chemical changes to yield an oxidation product, [Au(SCN)(2)](-), with an absorption maximum at 320 nm. The spectral changes associated with the chemical interaction between SiO2/Al2O3-stabilized gold nanoparticles and (SCN)2(.-) are elucidated using time-resolved transient absorption spectroscopy.