An experimental study of the collisional broadening of the Na- D lines by Ar and N 2 perturbers in flames and vapor cells—II. The line wings

Abstract

In this paper, we report on measurements of the fluorescence-excitation profile of the red Na- D 1 line wing from about 1 cm −1 to 1100 cm −1 and of the blue Na- D 2 line-wing from about 1 cm −1 to 600 cm −1, with respect to the corresponding line centre. We have also measured the fluorescence-excitation profile of the red Na- D 2 and blue Na- D 1 inner (overlapping) line wings from 1 cm −1 with respect to the centre of each of the lines. All these wings were measured in several premixed, laminar, shielded H 2O 2Ar and H 2O 2N 2 flames at 1 atm (1400 K ⪅ T ⪅ 2300 K). We also measured these wings in a vapor cell containing Ar or N 2 perturbers ( T ∼ 480 K, p ∼ 0.4 atm) in order to determine the influence of temperature on these wings. Using a tunable CW dye laser as excitation source, we determined the fluorescence-excitation profiles by measuring the total fluorescence intensity while tuning the laser wavelength. In order to specify the contributions that the different kinds of major flame perturbers (Ar, N 2, H 2O) make to the wings, we compared the wing profiles measured in various flames of different flame-gas compositions. In this comparison, the wing profiles were normalized with respect to the line-centre. We compared our measurements of far red Na- D 1 and blue Na- D 2 line-wings ( Δσ ⪆ 30 cm −1 ) specified to Ar perturbers (at T = 500 K and T = 2000 K) with the results derived from quasi-static theory using available interaction potential data. In the case of Ar perturbers at T = 500 K, we observed a satellite at about 8 cm −1 from the line-centre on the red Na- D 1 wing: this satellite was absent at T = 2000 K. The position of this red satellite was explained with the help of a set of “modified” potentials, which were constructed for interpreting the collisional Na- D broadening- and shift-rates deduced from our line-core observations and which were reported in Part I of this paper.