[FePAH]⁺ complexes and [Fe_xPAH_y]⁺ clusters in the interstellar medium: stability and spectroscopy

¹ Université de Toulouse, UPS, LCPQ (Laboratoire de Chimie et Physique Quantiques), IRSAMC, 118 Route de Narbonne, 31062 Toulouse, France
² CNRS, LCPQ, IRSAMC, 31062 Toulouse, France
³ Université de Toulouse, UPS, Centre d’Étude Spatiale des Rayonnements (CESR), Observatoire Midi-Pyrénées, 9 AV. Colonel Roche, 31028 Toulouse Cedex 04, France
⁴ CNRS, CESR, 31028 Toulouse, France

Abstract

The relevance of organometallic complexes in the chemistry of the interstellar medium (ISM) was first suggested in the early 90s. This initial proposal has recently been re-considered in the light of new astronomical data, benefiting from pioneering experimental techniques and theoretical methods. In this article, a review of recent theoretical and experimental results obtained for PAHs coordinated to Fe atoms is presented, focusing on: -(i)- the IR spectra of [FePAH]⁺ and [Fe(PAH)₂]⁺ complexes, found to be in line with the AIBs, with additional specific features in the far-IR range and -(ii)- the photo-evaporation of [Fe_xPAH_y]⁺ clusters as possible candidates for very small grains releasing PAHs in photodissociation regions. These results call for new astronomical data at high spatial resolution. Studies on larger clusters will require further experimental and theoretical developments.