EXAFS MEASUREMENTS FOR DENSE VAPORS OF CHALCOGENS AND CHALCOGENIDES

We have measured the EXAFS spectra of dense Se vapor in the temperature-pressure range up to 1600-degrees-C and 150 bar. For the measurements we have developed a high-pressure vessel and a polycrystalline sapphire cell of our own design. We have found that dense Se vapor under the present experimental condition consists mainly of Se2. The bond length is much shorter than that of liquid Se, and nearly the same as the data for Se2 in low-density vapor Se obtained by the recent spectroscopic study. When the saturated vapor-pressure curve is approached, the bond is elongated. We have also measured the EXAFS spectra of vapor Te and AsS. We have found the bond length of the molecule in vapor Te is nearly equal to that for Te2 obtained from the spectroscopic data. The structural parameters of the molecules in vapor AsS is similar to those of cage-like As4S4 molecules in the crystal with a monoclinic form.