Accurate determination of molecular structures by x-ray absorption spectroscopy

High-quality x-ray absorption fine structure (XAFS) spectra of the Br2, GeCl4, and BBr3 molecules, collected at a third generation synchrotron radiation source above the Br or Ge K-edges, are presented. Excellent fits are obtained using model spectra calculated in the muffin-tin approximation assuming Gaussian atomic distributions. The extended energy ranges of the spectra (up to 24 Å−1 for Br2) contribute to the reduction of the statistical errors in the structural parameters. We show that the potential accuracy of present XAFS determinations is 0.001 Å in bond lengths and 0.0001 Å2 in vibrational amplitudes. These results demonstrate that XAFS is nowadays competitive with electron diffraction in the determination of simple molecular structures in the presence of heavy atomic species.