STRUCTURAL INVESTIGATION OF GASEOUS, LIQUID, AND SOLID BR-2 BY X-RAY-ABSORPTION

Br K-edge x-ray-absorption measurements have been performed on gaseous (300 K), liquid (294 and 278 K), and solid (200 and 80 K) Br-2. The e xperimental data have been analyzed by using a comparison with calcula ted ab initio structural signals. The molecular Br-Br average distance , determined with the accuracy of 0.003 Angstrom A, shows an expansion of about 0.02 Angstrom A going from the gas phase to the low-temperat ure condensed phases. The bond-distance variance is found to be 2.0 x 10(-3) Angstrom A in the gas and liquid phases. The intermolecular con tribution in the condensed phases, which is found to affect considerab ly the near-edge region fo the spectrum kappa < 3.5 Angstrom A(-1), ha s been isolated by means of a subtraction procedure. Significant diffe rences between the liquid samples at the two temperatures are observed and the potential of these measurements to provide information on ori entational correlations between neighboring molecules is addressed.