orientation of the spin axis of electron, assuming that it is firmly oriented in space - this is called rigid top approximation. The magnetic moment of the nucleus is thousands of times smaller than the electron's, so such hyperfine corrections can be neglected in basic models. Finally the basic considered Lagrangian for dynamics of a single electron in these models is: The last term describes the interaction between the magnetic field of the traveling electron's magnetic moment and the electric field of the nucleus (spin–orbit interaction). Bates and Snyder examined the free-fall model and found it unsatisfactory. Primary sources References External links Michal Gryzinski webpage with lectures 20th-century Polish physicists 1930 births 2004 deaths