Journal of Physical Chemistry B, Vol.107, No.51, 14452-14456, 2003
Liquid-liquid phase separation and microscopic structure in rubidium-ammonia solutions observed using x-ray absorption spectroscopy
The phase behavior and microscopic structure of rubidium - ammonia (Rb-NH3) solutions have been measured below the consolute temperature (T-C = 209 K), using the extended X-ray absorption fine structure (EXAFS) technique. The use of an X-ray video camera provides us with the first direct evidence for liquid-liquid-phase separation of metallic (concentrated) and nonmetallic (dilute) Rb-NH3 solutions. Our real-time X-ray imaging also gives an extraordinary glimpse of the dynamic nature of the interior liquid-liquid interface, from which bubbles of ammonia vapor "boil" without disturbing the external meniscus. Analysis of the EXAFS structure measured above the Rb K-edge absorption at similar to 15.2 keV shows that the first solvation sphere of the cation is relatively broad, with similar to6.4 N atoms being located at a distance of 2.9-3.5 Angstrom. The location of the K-edge absorption for our solution is comparable with that measured for solid rubidium oxide, which is consistent with a Rb valency of +1 in our solution.