Laser-evaporated aluminum atom reactions with halogen molecules. Infrared spectra of AlX_n (X = F, Cl, Br, I; n = 1-3) in solid argon

Reactions of laser-evaporated aluminum atoms with molecular fluorine, chlorine, bromine, and iodine in excess argon during condensation onto a CsI window at 11 ± 1 K produced the AlX_n (X = F, Cl, Br, I and n = 1-3) and Al₂X₆ molecules, which were characterized by infrared absorption spectroscopy. Low laser power favored the primary reaction product AlX and AlX₂ transient species over the more stable secondary reaction product AlX₃ molecules. Chlorine and bromine isotopic structures substantiated the molecular identifications and vibrational assignments. DFT calculations were done for the AlCl_n and AlBr_n series to support the vibrational assignments. Possible Al₂Cl₄ structures were also explored by DFT calculations, and evidence is presented for a distorted Cl₂AlCl₂Al structure. The present study provides further evidence for transient aluminum dihalide radicals for the four halogens.