The x-ray absorption spectra (XAS) of Rb metal, Rh,("JH,J, ,, 2H-NbSe2Rb111x and RbBr near the Rb K-edge have been used to ascertain that the oxidation state V of rubidium dissolved in ammonia and intt:rcalated in the layer compound is in the range 0 < V < I. Theobservededge shifts with temperature for semimctals are explainedin terms of the population of band states, and the ratio of the density states near the mobility edge over that calculated for a free electron model, i.e. the Mott ratio g, is ascertained using a semiempirical relation developed for the x-ray absorbance from Is levels to empty states ncar the mobility edge.
Juana Vivó Acrivos, K. Hathaway, A. Robertson, M. P. Klein, and A. Thompson. "Mott g-Ratios in Rbx(NH3)1-x and Oxidation state of Rubidium Compounds from XAS" Journal of Physics C (1981): L557-L564. doi:10.1088/0022-3719/14/19/007