Extended x-ray absorption fine structure studies of dense selenium vapor

We have measured the extended x-ray absorption fine structure spectra for dense selenium vapor at high temperatures and pressures up to 1600 °C and 150 bar for the first time. For the experiment, we have developed a high-pressure vessel and a polycrystalline sapphire cell of our own design. We have found that dense selenium vapor under the present experimental condition consists mainly of Se2 and the bond length is much shorter than that of liquid Se. With increasing pressure the bond length slightly increases. When the saturated vapor-pressure curve is approached, the bond is largely elongated.