Missing Fe: hydrogenated iron nanoparticles

TL;DR

This paper proposes that hydrogenated iron nanoparticles, which may contain multiple H atoms, could explain certain spectral features and phenomena in the interstellar medium, including polarization and microwave emission.

Contribution

It introduces the concept of Fe-H nanoparticles as a new class of interstellar dust and provides computational spectra and formation conditions for these particles.

Findings

Hydrogenated iron nanoparticles exhibit broad infrared spectral bands.

Some Fe-H nanoparticles possess magnetic and electric moments.

Fe_nH_m particles could influence ISM polarization and microwave emission.

Abstract

Although it was found that the FeH lines exist in the spectra of some stars, none of the spectral features in the ISM have been assigned to this molecule. We suggest that iron atoms interact with hydrogen and produce Fe-H nanoparticles which sometimes contain many H atoms. We calculate infrared spectra of hydrogenated iron nanoparticles using density functional theory methods and find broad, overlapping bands. Desorption of H2 could induce spinning of these small Fe-H dust grains. Some of hydrogenated iron nanoparticles posses magnetic and electric moments and should interact with electromagnetic fields in the ISM. Fe_nH_m nanoparticles could contribute to the polarization of the ISM and the anomalous microwave emission. We discuss the conditions required to form FeH and Fe_nH_m in the ISM.