Complex organic molecules, including polycyclic aromatic hydrocarbons (PAHs), are found in a large variety of astronomical environments, including low temperature and low density molecular clouds in the interstellar medium which are the birthplaces of new stars and planets. Laboratory astrophysical studies on chemical reaction pathways under astronomically relevant conditions are crucial to interpret astronomical observations and as input for simulations in astrochemical networks. Of similar importance are spectroscopic studies of the often elusive, but essential, molecular reaction partners, intermediates and products that yield fundamental insights on their structure, and provide spectroscopic signatures needed for their identification in space. Cryogenic ion traps have proven to be ideal tools for studying ion-molecule reactions under controlled conditions and enable sensitive spectroscopic studies of mass-selected, cold, and isolated molecular ions. Here, I will describe the combination of such a cryogenic 22-pole ion trap instrument with the widely tunable infrared free electron lasers at the FELIX Laboratory [1]. Infrared action-spectroscopy is used to structurally characterize isomeric ions formed upon (dissociative) ionization of neutral species, allowing us to unravel their fragmentation processes (top-down processes). Very recently, we developed a novel combination of ion-molecule reactivity studies and infrared spectroscopy to elucidate and disentangle formation routes of complex molecules (bottom-up processes) at astronomically relevant temperatures, and have in this way identified an efficient low-temperature PAH-growth pathway from mono- to polycyclic aromatic hydrocarbons [2]. [1] P. Jusko, S. Brünken, O. Asvany, S. Thorwirth, A. Stoffels, L. van der Meer, G. Berden, B. Redlich, J. Oomens, S. Schlemmer, Faraday Discuss. 217, 172-202 (2019) [2] D.B. Rap, J.G.M. Schrauwen, A.N. Marimthu, B. Redlich, S. Brünken, Nat. Astron. 6, 1059 (2022)