Master‘s theses, 62 pages, 9 tables, 22 pictures, 19 literary resources, 2 appendixes, language – Lithuanian. Thesis includes important key words and concepts: rare-earth atom, energy, level, coupling, spectrum, electron, moment, Hund, Pauli, lanthanide. The purpose of this work – to analyse Praseodymium (Pr) and Holmium (Ho) and their ions energy level spectrum and analyses. Indoctrinate different coupling types, and give explanations of the rules how to definite terms. There are several problematical tasks set, to help in reaching this purpose: • analysis of the energy spectrum properties of lanthanides; • plotting of Pr and Ho and their ions energy levels from the experimental data; • analysis of Pr and Ho and their ions energy level plot and compare them; • presentation of fundamental theory of angular momentum; • traversing basic coupling types; • overview the definition of terms for each type of coupling. Thesis contains six chapters and two appendices. In the first chapter the periodic table is presented, together with the electron distribution in atoms and the filling of the electron shells. Shortly, the basic properties of lanthanides are introduced as well. In the second chapter the analysis of the multi-electron atomic spectra are analysed. In the third chapter the basic rules of addition of moments are presented. The fourth and the fifth chapter include studies of coupling types and rules for the calculation of the terms of one-electron , two-electron and... [to full text]