We report the occurrence of electron trapping by HOH center dot center dot center dot O=P(OR)(3) complexes in tri-n-butylphosphate (TBP) containing <0.4 mole fraction of water. This trapping shifts the absorption band of the electron to the blue with respect to neat TBP solvent, as the prevalent mode of electron solvation changes from that by aliphatic chains of TBP to that by dangling hydroxyl groups of the water-TBP complexes. In parallel, the rates of dissociative electron attachment to TBP and added scavenger both decrease. The structure of the trapping site is similar to that of the small, internally trapping water cluster anions in the gas phase. (C) 2008 Elsevier B.V. All rights reserved.