Precise predictions of H 2 O line shapes over a wide pressure range using simulations corrected by a single measurement

Abstract

In this work, we show that precise predictions of the shapes of H2O rovibrational lines broadened by N2, over a wide pressure range, can be made using simulations corrected by a single measurement. For that, we use the partially-correlated speed-dependent Keilson-Storer (pcsdKS) model whose parameters are deduced from molecular dynamics simulations and semi-classical calculations. This model takes into account the collision-induced velocitychanges effects, the speed dependences of the collisional line width and shift as well as the correlation between velocity and internal-state changes. For each considered transition, the model is corrected by using a parameter deduced from its broadening coefficient measured for a single pressure. The corrected-pcsdKS model is then used to simulate spectra for a wide pressure range. Direct comparisons of the corrected-pcsdKS calculated and measured spectra of 5 rovibrational lines of H2O for various pressures, from 0.1 to 1.2 atm, show very good agreements. Their maximum differences are in most cases well below 1%, much smaller than residuals obtained when fitting the measurements with the Voigt line shape. This shows that the present procedure can be used to predict H2O line shapes for various pressure conditions and thus the simulated spectra can be used to deduce the refined line-shape parameters to complete spectroscopic databases, in the absence of relevant experimental values.

Recent advances in collisional effects on spectra of molecular gases and their practical consequences

“…3.3.4). The resulting line shapes are in excellent agreement with those measured for many transitions of pure H 2 O and H 2 O in N 2 , under various pressure conditions [140][141][142][143]. It was in particular shown, using an empirical correction procedure similar to that applied to the CMDS predictions of CO line-shapes (cf [125] and Sec.…”

Prediction of high-order line-shape parameters for air-broadened O2 lines using requantized classical molecular dynamics simulations and comparison with measurements

“…The measured spectra of Ref. [18] of air-broadened 16 O2 lines in the singlet  band [ ] were retained here for validation of the procedure that we have proposed. Measurements were made at room temperature and for various pressures ranging from 6.7 kPa to 100 kPa (Table 1).…”

“…In [15,16], it was shown that first-principles calculations based on molecular configurations and intermolecular potentials, combined with a limited amount of information obtained from measurements successfully predicts the shapes of CO and H2O ro-vibrational lines. Indeed, these theoretical calculations are based either on classical molecular dynamics simulations (CMDS) [15] or a combination of CMDS and semi-classical methods (see [16] and references therein). It was shown that the non-Voigt effects observed in the measured spectra are well predicted by these first-principles calculations, for various molecular systems (e.g.…”

“…[17][18][19][20][21][22]) although the difference between the computed and measured line widths could be several percent. In [15,16], the calculations were thus empirically improved by introducing a measured value of the line width into the computed auto-correlation function of the transition dipole moment, where the line-shape equals the Fourier-Laplace transform of the latter quantity. With this correction procedure, it was shown that the calculations can predict measured spectra of several lines of CO [15] and H2O [16] over a large pressure range to within 1 %, significantly better than the best fits of the measurements with the usual Voigt profile.…”

“…In [15,16], the calculations were thus empirically improved by introducing a measured value of the line width into the computed auto-correlation function of the transition dipole moment, where the line-shape equals the Fourier-Laplace transform of the latter quantity. With this correction procedure, it was shown that the calculations can predict measured spectra of several lines of CO [15] and H2O [16] over a large pressure range to within 1 %, significantly better than the best fits of the measurements with the usual Voigt profile. In this work, first-principles CMDS calculations of line-shapes were used to provide theoretical spectra from which high-order line-shape parameters could be retrieved.…”