Spin-orbit coupling describes a process in which an
electron changes simultaneously its spin and angular
momentum or, in general, moves from one orbital wave
function to another. The mixing of the spin and the or-bital motion is a relativistic effect, which can be derived
from Dirac’s model of the electron. The mixing is large
in heavy ions, where the average velocity of the elec-trons is higher. Carbon is a light atom, and the spin orbit
interaction is expected to be weak.