Recent technical developments of X ray absorption spectroscopy (XAS) enable us to measure in situ/operando transmission spectra of liquid samples in the soft X ray region. We have discussed how various inter molecular interactions around the core excited atom are analyzed from the chemical shifts in XAS for the chemical state analysis of interacting molecular systems. We have newly developed liquid ‰ow cells for XAS in transmission mode, where liquid samples are sandwiched between two 100

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... thick Si 3 N 4 (or SiC) membranes in vacuum or in helium atmosphere. In order to get reliable XAS spectra, our XAS system makes it possible to optimize the absorbance by simply controlling the liquid sample thickness from 20 nm to 2000 nm, and also makes it possible toˆnd the region of uniform thickness by scanning the beam position on sandwiched liquid samples.