  We present a theoretical analysis of optical pathways for formation of cold
Ca($^1$S)Na$^+$($^1$S) molecular ions via an intermediate state. The formation
schemes are based on ab initio potential energy curves and transition dipole
moments calculated using effective-core-potential methods of quantum chemistry.
In the proposed approach, starting from a mixture of cold trapped Ca$^+$ ions
immersed into an ultracold gas of Na atoms, (NaCa)$^+$ molecular ions are
photoassociated in the excited E$^{1}\Sigma^+$ electronic state and allowed to
spontaneously decay either to the ground electronic state or an intermediate
state from which the population is transferred to the ground state via an
additional optical excitation. By analyzing all possible pathways, we find that
the efficiency of a two-photon scheme, via either B$^{1}\Sigma^+$ or
C$^{1}\Sigma^+$ potential, is sufficient to produce significant quantities of
ground state (NaCa)$^+$ molecular ions. A single-step process results in lower
formation rates that would require either a high density sample or a very
intense photoassociation laser to be viable.
