The two infrared-active vibrational bands of the 3 ν 3 manifold of SiF 4 were recorded at T ∼ 155 K with Doppler-limited resolution using a tunable laser difference-frequency spectrometer. Although all branches of the l = 1 band were seen, only portions of the P branch of the weaker l = 3 band were recorded. Some 192 lines with J ≤ 36 have been fitted to a model Hamiltonian which allows the l = 1 and l = 3 bands to interact. This analysis allows us to determine the effective harmonic frequency, ω 3 0, and the three anharmonic coefficients X 33, G 33, and T 33 with high precision, so that the vibrational levels in the nν 3 ladder can be predicted accurately for several values of n. In contrast with SF 6, the l basis is found to be the best representation for the vibrational sublevels.