Solar hydrogen lines in the infrared

We study recently observed H I lines in the infrared solar spectrum, employing detailed NLTE modeling to explain their formation and to evaluate their diagnostic merits. The solar infrared H I lines vary much in character, depending on opacity and wavelength; our computations reproduce the observations closely. The line wings are primarily set by Stark broadening due to metal ions and protons; the line cores are sensitive to NLTE population departure divergence which is driven by Balmer-continuum photoionization. The formation heights of the H I lines range from the deep photosphere for near-infrared line wings to the chromosphere for line cores with wavelengths greater than 10 microns; these features provide valuable diagnostics of the thermal structure of the solar atmosphere.