Helen Thompson,† Jonathan C. Wasse,† Neal T. Skipper,*,† Shusaku Hayama,†,§ Daniel T. Bowron,‡ and Alan K. Soper‡ Contribution from the Department of Physics and Astronomy, UniVersity College London, Gower Street, London WC1E 6BT, United Kingdom, and Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, United Kingdom Received September 30, 2002 ; E-mail: n.skipper@ucl.ac.uk
The technique of hydrogen/deuterium isotopic substitution has been used to extract detailed information concerning the solvent structure in pure ammonia and metallic lithium-ammonia solutions. In pure ammonia we find evidence for approximately 2.0 hydrogen bonds around each central nitrogen atom, with an average N-H distance of 2.4 Å. On addition of alkali metal, we observe directly significant disruption of this hydrogen bonding. At 8 mol % metal there remains only around 0.7 hydrogen bond per nitrogen atom. This value decreases to 0.0 for the saturated solution of 21 mol % metal, as all ammonia molecules have then become incorporated into the tetrahedral first solvation spheres of the lithium cations. In conjunction with a classical three-dimensional computer modeling technique, we are now able to identify a well-defined second cationic solvation shell. In this secondary shell the nitrogen atoms tend to reside above the faces and edges of the primary tetrahedral shell. Furthermore, the computer-generated models reveal that on addition of alkali metal the solvent molecules form voids of approximate radius 2.5-3.0 Å. Our data therefore provide new insight into the structure of the polaronic cavities and tunnels, which have been theoretically predicted for lithium-ammonia solutions
EFS Comments: We now understand the process of pumping and even binding the LEEF fuel to the NG to create excited and stable species of RM of which the constituents are fusible under modest conditions.
