Last hour: Orbit magnetism Classical picture: electron orbiting nucleus acts like a current loop, generating magnetic dipole moment For orbiting electron: With definition of the Bohr magneton as the magnitude of the magnetic moment generated by an electron with angular momentum ħ:

Consequence: replace with . Transformation of reference frame from nucleus at rest (left) to electron at rest (right). Consequence: replace with . (from Haken & Wolf “Atom- und Quantenphysik”)

Fine structure splitting in the Na 2P term no spin-orbit interaction spin-orbit interaction 2P3/2 a/2 2P -a 2P1/2

Learning Goals for Chapter 21 – Atomic Structure and Term Values After this chapter, the related homework problems, and reading the relevant parts of the textbook, you should be able to: assign configurations, terms and levels to the appropriate parts of the Hamiltonian of a multielectron atom; couple angular momenta in a multielectron atom; explain the assumptions made in LS coupling and in JJ coupling; construct atomic term symbols and qualitatively evaluate their relative energies; calculate the magnetic moment of an atom and its spin and orbital parts; explain the relation between magnetic moment and angular momentum; construct the Hamiltonian for atoms in external magnetic or electric fields.