Collisional narrowing: its effect on the equivalent widths of spectral lines.

A simple criterion is derived in terms of molecular parameters to determine whether collisional narrowing is of importance in determining the equivalent widths of spectral lines of any combination of emitting and broadening gases. The criterion is verified by numerical integration, and a simple formula is given for the maximum error obtained when the Voigt profile is used as an approximation to the Galatry profile.