On the s-d interaction in neon

The quadrupole and exchange interactions representing the short-range electron-ion scattering process have been observed and determined via the measurements of p 5 s and p 5 d, J=0 and 1 highly excited Rydberg states in Ne. The quantitative determinations were made possible by the combination of high precision (better than 100 MHz) perturbation-free measurements and multichannel quantum defect theory. A new precise value for the fine-structure splitting of the 20 Ne + (2p 5 ) ion is determined to be 780.4269(36) cm -1 .