Collisional narrowing effects on spectral line shapes measured at high resolution

Abstract

The averaging effect of velocity-changing collisions reduces the Doppler broadening of isolated spectral lines and leads to one type of collisional narrowing. We present four collisionally narrowed profiles in standardized form using dimensionless parameters and estimate the quantitative effect of narrowing on the spectral line shape in terms of the magnitudes of these parameters. We show that a collisionally narrowed profile fitted by a Voigt function exhibits a characteristic signature on a plot of the residual errors in the fit. This provides a simple test for detectable narrowing effects. One of the simpler and better known models which includes collisional narrowing is the Galatry profile. We present sample plots of the residual errors resulting when theoretical profiles computed from other more elaborate models are fitted by a Galatry function.