Plasmons in lithium ammonia

We report inelastic x-ray scattering measurements of the energy, linewidth, and dispersion of the plasmon in metallic lithium ammonia at an electron c oncentration of 4 x 10(21) e(-)/cm(3). These are the first measurements of plasmons in this system, which has the lowest electronic density for which a metal plasmon has been studied. We find a plasmon whose dispersion is onl y slightly reduced from the RPA value, and which is quite broad with an unu sual momentum dependence.