Dispersive XAFS Study on the Laser-Induced Reduction of a Rh ion complex; Presence of a Rh Intermediate in Direct Photoreduction
Saeki, Morihisa*; Matsumura, Daiju ; Nakanishi, Ryuzo*; Yomogida, Takumi ; Tsuji, Takuya ; Saito, Hiroyuki*; Oba, Hironori*
The reaction mechanism of the direct photoreduction of a Rh ion complex to a Rh species induced by pulsed ultraviolet laser irradiation was studied using dispersive X-ray absorption fine structure (DXAFS) spectroscopy. The time-resolved X-ray absorption near edge structure (XANES) showed the absence of isosbestic points and suggested that more than two Rh species contribute toward the direct photoreduction of Rh. Analysis of the time-resolved XANES data by singular value deposition showed that the direct photoreduction involves three Rh species. Multivariate curve resolution by alternating least-squares analysis (MCR-ALS) of the time-resolved XANES data gave pure spectra and concentration profiles of the three Rh species. The Rh species were assigned to Rh, Rh, and Rh species based on the features of the pure XANES spectra. The concentration profiles suggested that the direct photoreduction proceeds in the order of Rh Rh Rh. A reaction mechanism, which was proposed involving photoreductions of Rh and Rh, photoinduced autocatalytic reductions of Rh and Rh, and photooxidation of Rh, well reproduced the concentration profiles of three Rh species.