The reaction mechanism between AlX and HX (X = Br, Cl, and F) have been characterized in detail using DFT as well as the ab initio method. The reaction yielding AlX3 and molecular hydrogen was calculated to be highly exothermic. The present calculations also show that the possible routes to the trihalides species start more favorable with the primary insertion product AlX2H than with the biadduct AlX(HX)2 one.
 H.J. Himmel, J. Bahlo, M. Haussmann, F. Kurth, G. Stŏsser, H. Schnŏckel, Inorg. Chem. 41, 4952 (2002) http://dx.doi.org/10.1021/ic020275a
 Diatomic molecules: K.P. Huber, G. Herzberg, Constants of Diatomic Molecules (Van Nostrand, New York, 1979); (b) AlF3: M. Hargittai, M. Kolonits, J. Tremmel, J.-L. Fourquet, G. Ferey, Struct. Chem. 1, 75 (1989); (c) AlCl3 and AlBr3: K. Aarset, Q. Shen, H. Thomassen, A.D. Richardson, K. Hedberg, J. Phys. Chem. A 103, 1644 (1999)