Direct observation of a hydroperoxide surface intermediate upon visible light-driven water oxidation at an Ir oxide nanocluster catalyst by rapid-scan FT-IR spectroscopy.

A surface hydroperoxide intermediate has been detected upon oxidation of water at an Ir oxide nanocluster catalyst system under pulsed excitation of a [Ru(bpy)(3)](2+) visible light sensitizer by recording of the OO vibrational mode at 830 cm(-1). Rapid-scan FT-IR spectroscopy of colloidal H(2)O, D(2)O, and D(2)(18)O solutions in the attenuated total reflection mode allowed spectral assignment of IrOOH on the basis of an observed D shift of 30 cm(-1), and (18)O shifts of 24 cm(-1) ((16)O(18)O) and 46 cm(-1) ((18)O(18)O). The laser pulse response of the infrared band is consistent with the kinetic relevancy of the intermediate. This is the first observation of a surface intermediate of oxygen evolution at an Ir oxide multielectron catalyst.