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We investigate theoretically the circular polarization signals induced by theZeeman effect in the Fe II lines of the 279.3-280.7 nm spectral range of theCLASP2 space experiment and their suitability to infer solar magnetic fields.To this end, we use a comprehensive Fe II atomic model to solve the problem ofthe generation and transfer of polarized radiation in semi-empirical models ofthe solar atmosphere, comparing the region of formation of the Fe II spectrallines with those of the Mg II h and k and the Mn I resonance lines. These arepresent in the same near ultraviolet (near-UV) spectral region and allowed themapping of the longitudinal component of the magnetic field ($B_{\rm L}$)through several layers of the solar chromosphere in an active region plage. Wecompare our synthetic intensity profiles with observations from the IRIS andCLASP2 missions, proving the suitability of our model atom to characterizethese Fe II spectral lines. The CLASP2 observations show two Fe II spectrallines at 279.79 and 280.66 nm with significant circular polarization signals.We demonstrate the suitability of the Weak-Field Approximation (WFA) applied tothe Stokes $I$ and $V$ profiles of these Fe II lines to infer $B_{\rm L}$ inthe plage atmosphere. We conclude that the near-UV spectral region of CLASP2allows to determine $B_{\rm L}$ from the upper photosphere to the top of thechromosphere of active region plages.

Magnetic field information in the near-ultraviolet Fe II lines of the CLASP2 space experiment