The configuration interaction in the odd states of the copper atom and its effects on energy levels and transition probabilities have been studied with the multiconfiguration Hartree-Fock method. Relativistic effects have been included to first order. Good agreement is found between the results of the present work and available experimental data. The origins of observed irregularities in the energy-level structure and lifetime trends are explained. Properties of importance for the possible generation of additional lines in the copper-vapor laser are discussed. I. INTRODUCTION The electronic structure of the copper atom is similar to that of the potassium atom but copper has ten addi- tional electrons. In the ground state these occupy the 3d shell. The ground state of copper, as of potassium, is 4s S, &2 and copper has the same nl L Rydberg series as the alkali-metal atoms. An energy-level diagram of the copper atom is shown in Fig. 1. The presence of the 3d electrons causes a number of effects which are not found in the alkali-metal atoms and which make theoretical cal- culations for the copper atom rather more complicated. Since the 3d orbitals are more extended in space than the 3p or other inner-shell orbitals, the 3d shell is more strongly inAuenced by the valence electron. This effect is different in different states. Therefore, in a theoretical calculation, it will be a much too crude approximation to include the 3d shell in a fixed core. On the other hand, not to include it and treat copper as an eleven electron problem, would make the calculations impractical. The energy needed to excite an electron from a 3d to a 4s or 4p state is less than the ionization energy, so, in ad- dition to the 3d' nl L states copper has a number of bound state belonging to the configurations 3d 4s and 3d 4s4p. These may interact with states in the 3d' nl L Rydberg series. The 3d 4s configuration gives rise to a D term only, which is situated far below any of the 3d' nd D states with which it could possibly interact. The 3d 4s4p configuration gives rise to nine different terms' of which 3d 4s( D)4p P, D, F, P, D, and F