  For the electromagnetic interaction of two particles the relativistic quantum
mechanics equations are proposed. These equations are solved for the case when
one particle has a small mass and moves freely. The initial wave functions are
supposed to be concentrated at the coordinates origin. The energy spectrum of
another particle wave function is defined by the initial wave function of the
free moving particle. Choosing the initial wave function of the free moving
particle it is possible to obtain a practically arbitrary energy spectrum.
