Core-Electron Splittings and Hyperfine Fields in Transition-Metal Compounds

$2s$ and $3s$ core-electron exchange splittings have been measured for a number of transition-metal compounds. It is found that the $2s$ splittings agree roughly with values from Hartree-Fock calculations, whereas measured $3s$ splittings are smaller by about a factor of 2. This discrepancy is tentatively linked to correlations connected with the hole produced by the photoelectric process. A comparison of exchange splittings with hyperfine fields in spin-only compounds suggests a close relationship between these two properties.