Identifications of the species responsible for the unidentified interstellar infrared (UIR) emission bands and the diffuse interstellar absorption (DIB) bands are the two of the major challenges in astrochemistry today. Polycyclic aromatic hydrocarbons (PAHs) have been proposed as the carriers of both signals. Carbon chain clusters and metals have both been detected in the interstellar medium. In this dissertation, reactions of iron with PAHs, and metals (copper, silver and gold) with carbon clusters were investigated. Matrix isolation spectroscopy coupled with density functional (DFT) calculations have been employed throughout this research.

Laser ablated iron atoms and evaporated or sublimed benzene, naphthalene, fluorene, pyrene, or coronene were trapped together in solid Ar at 12K. Neutral Fe(benzene), Fe(benzene)₂, Fe(naphthalene), Fe(fluorene), Fe(pyrene) and Fe(coronene) complexes were formed in the experiments and their infrared absorption spectra obtained. Theoretical calculations of the equilibrium geometries, stabilities, and harmonic vibrational frequencies of these complexes have been carried out using density functional theory. The calculations show that the dissociation energies (D₀) of neutral Fe(PAH) complexes are substantially smaller than their cationic counterparts, indicating that the neutral complexes are less tightly bonded.

Reactions of laser-ablated metal (copper, silver and gold) atoms with carbon clusters were investigated in excess argon matrices. Fourier transform infrared absorption spectra, with the assistance of ¹³C-isotopic substitution experiments and comparison with theoretical calculation, have led to the identification of near-linear CuC₃, AgC₃ and AuC₃ clusters. Photo-induced isotopic scrambling was observed in the Cu¹²¹³C₃ clusters and explained via a computed potential energy surface (PES) of this reaction. The mechanism for the photoscrambling is shown to involve the formation of a bicyclic CuC₃ isomer. The formation of small metal-carbon clusters, Cu_mC_n and Ag_mC_n (m=1, 2; n=1-3) were also explored theoretically.