In systems with multiple
electrons within an LS coupled subshell, terms with high S and
low L tend be the most tightly bound.
Low L means elliptic orbits,
which spend more time close to the nucleus.
WHY HIGH S ?
High values of S occur
when the electron spins are aligned (all have the same ms),
causing the spin portion of the wave function to be symmetric.
The space portion of the wave
function must then be antisymmetric, and the Pauli exclusion principle prevents
the equivalent electrons from occupying the same region of space.
Thus the inter-electron
repulsion is reduced thereby increasing the binding.
CONCLUSION: A Bose condensation in spin-space produces a
Pauli exclusion in configuration space.
WHEREAS FOR LOW S,
For systems with low S, the
spins are anti-aligned pairwise, with anti-symmetric wave functions.
Thus the spatial wave function
is symmetric and the equivalent electrons can overlap in space, increasing
their repulsive interaction.
CONCLUSION: A Pauli exclusion in
spin-space produces a Bose condensation in configuration space.
The high S of the ground state
has implications in, eg, the high spin magnetism in the partially filled 3d
shell of ferromagnetic atoms.