Analytical approximations for speed-dependent spectral line profiles

Analytical approximate expressions for speed-dependent Rautian-Sobel'man, Voigt, and general line profiles, including spectral line mixing, were obtained. Systematic errors of the approximate profiles are within 0.7% for the mass ratios of perturbing and absorbing molecules mb/ma≤9. The calculation time of the approximate line profiles is much shorter than the time required for calculating exact expressions for the line profiles. An approximate analytical expression for the observable homogeneous line width was derived. A least-square fitting of the singlet methane absorption line centered at 6107.17 cm−1 was performed, using the approximate line profiles obtained.

► Analytical expressions for speed-dependent line profiles were obtained. ► Systematic errors of the approximate profiles are within 0.7%. ► Observable homogeneous line width nonlinearly depends on the gas pressure. ► Systematic errors of the Voigt line profile were determined. ► Line profiles developed provide retrieving reliable spectral line parameters.