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fast communications
The X-ray absorption spectra of GaCl2, GaAlCl4 and GaCl3 have been measured in the vicinity of the Ga K edge and values of f'' and f' estimated for GaI and GaIII from the latter two spectra by using the optical theorem and the Kramers-Kronig relation. The resulting f' values are compared with those previously determined from anomalous-scattering measurements with synchrotron X-rays on the compound GaCl2 [Wilkinson, Cheetham & Cox (1991). Acta Cryst. B47, 155-161] and found to be in good agreement. The use of anomalous scattering methods for distinguishing oxidation states is discussed in the light of these results and others found in the literature.