Toward Detection of FeH in the Interstellar Medium: Infrared Multiple Photon Dissociation Spectroscopy of ArFeH.

The iron hydride molecular cation FeH is expected to be present in the interstellar medium. Because of the lack of laboratory data, it is yet to be identified in spectrally resolved astronomic observations. As a benchmark for computational predictions and to guide an experimental search for the ro-vibrational lines of FeH, we performed infrared multiple photon dissociation (IRMPD) spectroscopy of FeH tagged with two argon atoms. The Fe-H stretching mode in ArFeH is observed at 1860 cm. Combination bands of the Fe-H stretch with the two Fe-H bending and the asymmetric Fe-Ar stretching modes are observed at 2012 cm, 2054 cm, and 2078 cm. Quantum chemical calculations show that the molecule has C symmetry. The Ar-Fe-Ar bending mode at 46 cm is significantly populated at the temperature of the experiment, causing thermal broadening of the Fe-H stretch and its redshift with increasing internal energy.