Pressure broadening and shift of 3.39-μ absorption in methane perturbed by noble gases

High-resolution tuned-laser spectroscopy was used to study pressure broadening and shift of a 3.39-μ methane absorption line perturbed by noble gases. Measurements were carried out in the low-pressure region where collisions influence the line shape both by pressure broadening and by narrowing the Doppler width. The Galatry line shape was found best suitable for determining the linewidth. In order to account for the observed ratio of line width to line shift, it was found necessary to modify Foley's phase-shift theory by adding a "hard-core" term to the collision cross section.