F -state interference significantly modifies the polarization produced by scattering processes in the solar atmosphere .
Its signature in the emergent Stokes spectrum in the absence of magnetic fields is depolarization in the line core .
In the present paper , we derive the partial frequency redistribution ( PRD ) matrix that includes interference between the upper hyperfine structure states of a two-level atom in the presence of magnetic fields of arbitrary strengths .
The theory is applied to the Na i D _ { 2 } line that is produced by the transition between the lower J = 1 / 2 and upper J = 3 / 2 states which split into F states because of the coupling with the nuclear spin I _ { s } = 3 / 2 .
The properties of the PRD matrix for the single-scattering case is explored , in particular , the effects of the magnetic field in the Paschen–Back regime and their usefulness as a tool for the diagnostics of solar magnetic fields .