  This work theoretically addresses the trapping an ionized atom with a single
valence electron by means of lasers, analyzing qualitatively and quantitatively
the consequences of the net charge of the particle. In our model, the coupling
between the ion and the electromagnetic field includes the charge monopole and
the internal dipole, within a multipolar expansion of the interaction
Hamiltonian. Specifically, we perform a Power-Zienau-Woolley transformation,
taking into account the motion of the center of mass. The net charge produces a
correction in the atomic dipole which is of order $m_e/M$ with $m_e$ the
electron mass and $M$ the total mass of the ion. With respect to neutral atoms,
there is also an extra coupling to the laser field which can be approximated by
that of the monopole located at the position of the center of mass. These
additional effects, however, are shown to be very small compared to the
dominant dipolar trapping term.
