Regularities in s-electron binding enegies in lNsM configurations*

We present a theoretical explanation for observed regularities in s -electron binding energies in lNs2 and lNs: viewed as a function of N, the curves form straight lines, joined continuously at the half-filled shell. The change in slope can be interpreted as an effective exchange integral Gl(l, s). We show that values of the exchange integral obtained from fitting ionization-energy curves generally agree with values obtained in other ways.