The effect of velocity-dependent collision broadening on the shape of spectral lines is investigated. Computations show that the modified line shape has a narrower half-width than the conventional Voigt profile.
B. W. Fowler and C. C. Sung, "Doppler and collision-broadening effects in the profile of spectral lines," J. Opt. Soc. Am. 65, 949-951 (1975)