Ab initio quantum mechanical vibrational analysis of planar AX(3) molecules (A is Al, Ga, In; X is F, Cl, Br, I)

Bond lengths and vibrational frequencies are calculated for the title compounds at the SCF level using various basis sets. For AlF3, AlCl3, AlBr3 and GaCl3 also MP2 calculations are included. For some of these molecules, in particular for their out-of-plane vibrations, it appears that the calculated values are very sensitive to the choice of basis sets, and in these cases the predictions from the calculations may be inaccurate. The calculations verify most of the assignments given in the literature; however, for several of the molecules a revision is suggested for nu(2)(A(2) '') and nu(4)(E'). A redetermination of the molecular structure of InCl3 appears to be useful.