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.