Collisional line shapes have been measured for the fundamental band transitions of I-IF in an Ar buffer gas at T=296 K using a tunable difference-frequency laser spectrometer. The broadening and shift coefficients are in excellent agreement with recent close-coupling scattering cross section calculations [Green and Hutson, J. Chem. Phys. 100, 891 (1994)] based on a realistic intermolecular potential surface determined by high-resolution infrared and microwave spectroscopy of the Ar-HF van der Waals complex. Below atmospheric pressure, the line shapes exhibit strong collisional (Dicke) narrowing of the Doppler distribution and a slight asymmetry which we model with hard collision (Rautian) or soft collision (Galatry) profiles modified for partial correlation between velocity- and state-changing collisions.