Figure 1.

Photo-reduction of a 1 mM buffered aqueous solution of sodium selenate (50 mM HEPES/NaOH pH 7.5, 20% v/v glycerol). The sample was measured on SSRL BL9-3 at 10 K using a PIPS Si detector to monitor fluorescence. (a) Superposition of four consecutive sweeps each separated by 6 min, illustrating increasing degrees of photo-reduction on a sweep-by-sweep basis. (b) Spectra corresponding to solutions of selenate and selenite. The spectra in (a) can be fitted well using a linear combination of selenite and selenate spectra (b) (not illustrated), suggesting that the photo-chemical reaction involves only these two species.