Electronic Structure of Sodium-Ammonia Solutions by Nuclear Magnetic Resonance

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Abstract
Knight shifts (ΔH) of the N14 and Na23 nuclear magnetic resonances have been observed in liquid sodium‐ammonia solutions at 7000 gauss as a function of the mole ratio R=(moles NH3)/(moles Na) for 10⪝R ⪝1000. The Knight shifts decrease with increasing R and for R≈10, ΔH(N14)≈4, ΔH(Na23)≈1 gauss. The experimental results in these variable composition solutions are conveniently discussed in terms of P(N14) and P(Na23), the average hyperfine contact densities of N14 and Na23 nuclei at an unpaired electron. P(N14) and P(Na23) were estimated from K–NH3 paramagnetic susceptibility data and the ΔH's. For 50<RP(Na23)=5–3×10—3 P0(Na23) where P0(Na23) is the contact density in an isolated sodium atom. In this concentration range we conclude the odd electrons move in highly expanded orbitals about Na+ ions similar to those appropriate to tetrahedrally bonded P+ ions in P‐doped silicon where a similar reduction in the contact hyperfine density is found. Marked electron condensation on Na+ ions occurs at R⪝50 where P(Na23) and the electrical conductivity increase rapidly. P(N14)≈0.1 P0(N14) and is independent of R. H1Knight shifts were too small to detect.