  Both the quality and amount of astrophysical data are steadily increasing
over time owing to the improvement of telescopes and their instruments. This
requires corresponding evolution of the techniques used for obtaining and
analyzing the resulting data. The infrared spectral range at 1.56 $\mu$m
usually observed by the GRegor Infrared Spectrograph (GRIS) at the GREGOR solar
telescope has a width of around 30 $\AA$ and includes at least 15 spectral
lines. Normally, only a handful of spectral lines (five at most) are used in
studies using GRIS because of the lack of atomic parameters for the others.
Including more spectral lines may alleviate some of the known ambiguities
between solar atmospheric parameters. We used inversion techniques to infer
both solar atmospheric models and the atomic parameters of spectral lines
which, under the local thermodynamic equilibrium (LTE) approximation, reproduce
spectropolarimetric observations. We present accurate atomic parameters for 15
spectral lines within the spectral range from 15644 $\AA$ to 15674 $\AA$. This
spectral range is commonly used in solar studies because it enables the study
of the low photosphere. Moreover, the infrared spectral lines are better
tracers of the magnetic fields than the optical ones.
