The geometries, relative energies, harmonic Vibrational frequencies, and infrared intensities of the two most prevalent [84] fullerene isomers are studied using density functional theory (B3LYP) and basis sets as large as 6-31G*. The D-2 and D2d-C84 isomers are found to be essentially isoenergetic. The computed infrared spectra are very sensitive to the basis set, and good agreement with the available experimental data is only obtained if the basis set includes polarization functions.