position or contraction of the energy levels of every specie with respect to its ground state. Our theoretical distribution of energy levels agrees completely with the experimental results [@NIST]. In addition we have determined in this work atomic levels which experimental values have not been yet reported, like states with $ L \ge 4$ in Li atom, $L \ge 6$ of Be$^+$ ion, $L \ge 7$ of C$^{3+}$ and $L \ge 4$ of F$^{6+}$ ion. Using theoretical and experimental results we can conclude that the order of the energy levels in the duplet states of the neutral atom and isoelectronic ions is $S <   P <   D <   F <   G <   H <   I <   K <   L <   M <   N <   \dots $

As is well known from basics of atomic spectroscopy (see, e.g., [@Sob]) all three-electron atoms and ions are observed in the two series of states: (a) doublet states with $S_e = \frac12$, and (b) quartet states with $S_e = \frac32$, where $S_e$ designates the total electron spin. The quartet states in these atomic systems are non-stable, i.e. they decay for relatively short times. Thus, the only bound states which are observed in actual spectroscopy 