It does not seem possible to account for the presence of singlets below their triplets in two electron spectra simply from the ordinary exchange integrals. The exchange integrals seem to be essentially positive. It is shown that the matrix component of electrostatic energy connecting the $3s3d{}_{}{}^1{}_{}{}^{}D$ with $3p^2{}_{}{}^1{}_{}{}^{}D$ in Mg I is sufficiently large to account for the occurrence of $3s3d{}_{}{}^1{}_{}{}^{}D$ below $3s3d{}_{}{}^3{}_{}{}^{}D$ as observed experimentally. Analytic radial wave functions of the type developed by Slater are used in the calculation of the nondiagonal elements.

• Received 16 December 1932

DOI:https://doi.org/10.1103/PhysRev.43.264