Knight Shifts and Relaxation Times of Alkali-Metal and Nitrogen Nuclei in Metal—Ammonia Solutions

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Abstract
Knight shifts of 7Li, 23Na, 87Rb, 133Cs, and 14N in alkali-metal—ammonia solutions have been measured at 300°K and in the concentration range 0.03 to 1 mole liter—1. 23Na NMR has been observed at Na concentrations down to 0.003 mole liter—1 at 300°K and in the range 0.03 to 4 mole liter—1 at 274° and 240°K. 14N shifts are reported for concentrations from 0.008 to 4 mole liter—1 at 300° and 240°K. Linewidths of 87Rb and 133Cs have been obtained at 300°K in the concentration range 0.03 to 0.8 mole liter—1. At 0.35 mole liter—1 and 300°K the shifts of Li, Na, Rb, and Cs are 9, 72, 450, and 900 ppm, respectively, to lower magnetic field. Shifts of 14N are nearly independent of metal at 300°K. The concentration and temperature dependence of 23Na Knight shift data at concentrations up to 0.4 mole liter—1 may be quantitatively interpreted by the following reactions: M⇌M++e−,M+e−⇌M−,where M represents the ``monomer'' species and (2) is the spin-pairing reaction. The 14N spin density at unpaired electron is essentially independent of alkali metal and concentration up to 0.6 mole liter—1 and equal to 0.88±0.11 a0—3 at 300°K. The electron spin density at 23Na is calculated to be ≥8×10—3 a0—3 approximately independent of temperature and concentration. The lifetimes of the Rb and Cs monomers at 300°K and 0.06 mole liter—1 are ≤3 and ≤4 μμsec, respectively, as determined from NMR linewidth measurements. The monomer lifetime decreases sharply with increase in metal concentration.