CHAP. 12: BASIC TERMS OF CHEMICAL PHYSICS [CONTENTS] 427
wherege= 2.0023193 is thespin g-factoralso calledgyromagnetic ratioof free electron
and the spin projection (magnetic quantum number)msadopts values from−stos, i.e.± 1 / 2
(cf. (12.29)).
Note:The nucleus itself may interact with an external magnetic field and it may also have
its own spin. An energy change caused by the interaction of the magnetic field with the
nucleus spin is
∆Enucl=gNmNmSB , (12.41)
wheregNis the nucleus g-factor,mS=−S,−S+ 1,... ,+S, whereSis the total spin
quantum number of the nucleus, andmNis the nuclear Bohr magneton, which is defined
similarly as in relation (12.39), only the electron mass is replaced by the nucleus mass.Complete calculation of the energy of atoms containing more electrons is very complicated.
The reason is that the potential energy in the Schr ̈odinger equation includes other terms such
as the mutual repulsion of electrons, and it can be solved only approximately. For every type
of atom there is nevertheless a unique set of possible energy states which can be taken up by
its electrons.