Isospin method for complex electronic configurations

It is shown that the isospin formalism is convenient for discussing the properties of the wavefunctions of the configurations n 1 l N1 n 2 l N2 with respect to the orthogonal transformations of the radial orbitals. The main point of this formalism consists of the statement that the existence of an electron in one of the two shells n 1 l N1 or n 2 l N2 is considered as the additional degree of freedom in some abstract 'isospin' space. The corresponding basis is defined and the properties of the wavefunctions and operators are studied in this basis. The authors analyse the conditions under which the isospin T may be a fairly exact quantum number for complex electronic configurations.