Ultrafast extended x-ray absorption fine structure (EXAFS) - theoretical considerations

Inspired by the recent experimental demonstration of ultrafast x-ray absorp tion spectroscopy, we present a framework for the calculation of extended x -ray absorption fine structure (EXAFS) spectra on the ultrafast (femtosecon d to picosecond) time scale. Model calculations for gas phase I-2, evolving under the influence of laser pumping, demonstrate that ultrafast EXAFS has the potential to serve as a direct probe of nuclear dynamics, including ti me-dependent interatomic separations and relative orientations. The feasibi lity of ultrafast EXAFS as a viable and useful experimental technique is di scussed. (C) 1999 American Institute of Physics. [S0021-9606(99)00338-4].