Oligomers of AlCl have been characterized. By using the matrix isolation technique, the dimer Al 2 Cl 2 , which exhibits a D 2h -symmetric ring structure, was generated in significant quantities and analyzed by its IR and Raman spectra in combination with quantum chemical calculations. The structures of the trimer and tetramer have also been evaluated. A surprising result is that the minimum energy structure of the trimer (C s symmetry) features direct Al-Al bonds, two terminal Al-Cl bonds, and one bridging Cl atom. A weak, isotopically structured IR band can be assigned to the antisymmetric ν(Al-Cl t ) mode of this trimer (Cl t denotes a terminal Cl atom). The enthalpy change for each of the oligomeriza-