Introduction

Abstract

The theory of angular momentum in quantum mechanics is central to atomic and nuclear physics. In applications of the theory, one deals with methods of coupling and recoupling states described by quantum numbers which contain, in most cases, angular momenta (spin and orbital) and and their projections.Pioneer work on the subject has been done during the first part of the 20^th century and a useful collection of reprints can be found in Biedenharn and Van Dam [1]. Of special note are applications of the theory to the interpretation of atomic spectra underpinned by the definitive contribution of Condon and Shortley [2] and, later, seminal work by Racah [3] that now is a bedrock of atomic and nuclear physics.