  Relativistic quantum mechanics of a Proca (spin-1) particle in Riemannian
spacetimes is constructed. Covariant equations defining electromagnetic
interactions of a Proca particle with the anomalous magnetic moment and the
electric dipole moment in Riemannian spacetimes are formulated. The
relativistic Foldy-Wouthuysen transformation with allowance for terms
proportional to the zero power of the Planck constant is performed. The
Hamiltonian obtained agrees with the corresponding Foldy-Wouthuysen
Hamiltonians derived for scalar and Dirac particles and with their classical
counterpart. The unification of relativistic quantum mechanics in the
Foldy-Wouthuysen representation is discussed.
