On the role of Dicke narrowing in the formation of atomic line shapes in the optical domain

Abstract

The purpose of this work is to verify the possibility of the observation of the Dicke narrowing of atomic spectral lines in the optical domain. As an example we have chosen experimental results obtained by means of a laserinduced fluorescence method for the 114 Cd 326.1 nm line perturbed by xenon. Experimental results were carefully reanalysed using a line shape model which takes into account the speed dependence of collisional broadening and shifting, the velocity-changing collisions and the collision-time asymmetry. We have found no convincing evidence for the occurrence of Dicke narrowing of the 326.1 cadmium line perturbed by xenon. The Dicke narrowing (if it occurs at all) appears to be smaller than that resulting from the estimation based on the accessible data describing the diffusion of Cd in Xe. As a source of this behaviour the correlation between velocity-changing and dephasing collisions was indicated.

Influence of the line-shape model on the spectroscopic determination of the Boltzmann constant

“…In our simulation, the NGP is the best, probably because it uses the same model of velocity-changing collisions as the SDNGP used here as a reference profile. In any experiment, the proper line shape could be found from analysis of spectra measured at a broader pressure range at which the speed-dependent effects, the Dicke narrowing, and different models of collisions can be distinguished [17,[36][37][38][39][40][41][42][43]. The multispectrum fit procedure [44] is a powerful tool for such analysis and allows one to deal with the problem of numerical correlations between fitted parameters of the line-shape model, as was demonstrated for more sophisticated profiles in Refs.…”

Dicke-narrowed spectral line shapes of CO in Ar: Experimental results and a revised interpretation

“…It is sometimes referred to as the (effective) velocity-changing collision rate. By convention, the narrowing parameter z is defined as m/x D , where x D = k(2k B T/m a ) 1/2 is the Doppler half width at e À1 intensity for wavevector k, Boltzmann constant k B , and temperature T. A common [2][3][4][5][36][37][38][39][40][41][42][43][44] approach to analyzing Dicke-narrowed line shapes is to fit for m and compare the result to the dynamic friction coefficient, m diff , which is obtained from the mass diffusion constant D by…”

“…There is growing experimental evidence that the effective collision rate m does not agree with m diff [1,3,16,31,[40][41][42][43][44].…”

Velocity-changing collisions in pure H2 and H2-Ar mixture

“…At present, to the best of our knowledge, the most realistic models describing velocity-changing collisions applicable in line shape calculation 19,24,25 and used for fitting of experimental data [25][26][27][28][29][30][31][32] are the billiard-ball (BB) model 19,33,34 and a bit more general Blackmore model, 19,35 which assumes repulsive inverse-power potential. The most important advantage of the BB model is that it allows to take into account the speed-dependence of frequency of velocity-changing collisions as well as the speed-and direction-changing collisions for a given perturber/absorber mass ratio in a proper way.…”