Toward measurements of the speed-dependence of line-mixing

Abstract

We theoretically demonstrate that some doublets of NH 3 broadened by Ar and heavier atoms may be suitable for the first experimental demonstration of a so-far unstudied problem: The spectral effects of the speed dependence of line-mixing. By using realistic assumptions and spectroscopic data from previous studies, we show that neglecting this process leads to errors on the spectral shape of up to 2% of the peak absorption value. When multispectrum fits are made assuming speed-independent line couplings, the peak-to-dip residuals amplitudes reduce to about 0.5% and 1% for NH 3 -Ar and -Xe, respectively. The magnitude of the effect is thus comparable to that of the speed dependence of the line broadening on isolated shapes, which has been demonstrated in many experimental studies. It should hence be detectable with high accuracy modern laboratory spectroscopic techniques. With this aim, guidelines and conditions paving the path for future experiments are given.

CO-Ar collisions: ab initio model matches experimental spectra at a sub percent level over a wide pressure range

“…The latter was evaluated and found to be negligible under our experimental conditions in accordance with conclusions of work Ref. [69]. The use of the speed dependent parameter Y (v) instead of the speed averaged value Y in calculations of the line shape (Eq.…”

A quantum study of argon induced line mixing in ammonia doublets

“…The perturbation of the spectra of ammonia in argon baths has lead to numerous studies [1][2][3][4][5][6][7][8][9][10][11]. Most of these studies dealt with the pressure broadening and shift coefficients but some also addressed the line mixing effect.…”

“…To our knowledge the speed dependence of the pressure broadening and shift has received little attention for this system [3,6,12] and the speed dependence of the line mixing completely disregarded. Recently, on the basis of the quadratic [13] or hypergeometric [14] models often used to model the speed dependence of the collisional broadening, Boulet et al [11] have suggested that the speed dependence of intradoublet coupling coefficients could be observed in the ν 4 band of ammonia in argon. In order to check this proposition we have performed dynamical calculations on a potential energy surface (PES) [15].…”