Time-resolved x-ray absorption spectroscopy on microsecond timescales: Implications for the examination of structural motions

We demonstrate a system for collecting high quality x-ray absorption spectroscopy data on microsecond and longer timescales. The method uses a fast-multiscaling board to partition output pulses from a germanium energy resolving detector into a microsecond timebase. Full spectra accumulation and kinetic spectrophotometry are demonstrated for 1–4 mM biological samples. The use of an energy resolving detector promises that the dynamic behavior of a wide range of chemical elements (in conjunction with photochemical, rapid mixing, and temperature jump perturbations) can be observed with this method. We have successfully tested the system by examining the structural evolution of the iron atom of a myoglobin-carbon monoxide complex subsequent to photolysis at low temperature.