Velocity effects on the shape of pure H2O isolated lines: Complementary tests of the partially correlated speed-dependent Keilson-Storer model

Abstract

Complementary tests of the partially correlated speed-dependent Keilson-Storer (pCSDKS) model for the shape of isolated transition of pure water vapor [N. H. Ngo et al., J. Chem. Phys. 136, 154310 (2012)] are made using new measurements. The latter have been recorded using a high sensitivity cavity ring down spectrometer, for seven self-broadened H(2)O lines in the 1.6 μm region at room temperature and for pressures from 0.5 to 15 Torr. Furthermore, the H(2) (18)O spectra of [M. D. De Vizia et al., Phys. Rev. A 83, 052506 (2011)] in the 1.38 μm region, measured at 273.15 K and for pressures from 0.3 to 3.75 Torr have also been used for comparison with the model. Recall that the pCSDKS model takes into account the collision-induced velocity changes, the speed dependences of the broadening and shifting coefficients as well as the partial correlation between velocity and rotational-state changes. All parameters of the model have been fixed at values previously determined, except for a scaling factor applied to the input speed-dependent line broadening. Comparisons between predictions and experiments have been made by looking at the results obtained when fitting the calculated and measured spectra by Voigt profiles. The good agreement obtained for all considered lines, at different temperature and pressure conditions, confirms the consistency and the robustness of the model. Limiting cases of the model have been then derived, showing the influence of different contributions to the line shape.

Progress towards the determination of thermodynamic temperature with ultra-low uncertainty

“…A fully quantum-mechanical treatment of spectral line shapes is very complicated, especially for self-colliding polyatomic molecules. Despite that, recent progress of modelling capabilities, even though in a semi-classical framework, has been one of the key elements leading to the recent achievements obtained by DBT [40]. So far, the best DBT implementation has been performed on H 2 18 O molecules, using a dual laser approach at a wavelength of 1.4 µm [41].…”

Absorption-line-shape recovery beyond the detection-bandwidth limit: Application to the precision spectroscopic measurement of the Boltzmann constant

“…If the influence of the time constant  D is considered via Eq. (11), that is assuming a linear evolution of the laser frequency, shifts of retrieved frequencies (plotted as +) are inverted. This feature cannot be explained only by a calibration error in  D (a factor about 2 would be required) and suggests the influence of the step-by-step spectrometer operation.…”

“…Similarly, the interpretation of spectra of astrophysical and planetary interest needs a precise knowledge of line-shape parametres and current databases require further improvements [6,7]. The accurate observation of line profiles is also crucial to the physics of collisions by testing theories modeling the shape of atomic or molecular transitions perturbed by collisions [8][9][10][11][12]. Highly accurate spectroscopy plays as well a decisive role in precision measurements devoted to metrological applications and tests of fundamental physics.…”

Recommended isolated-line profile for representing high-resolution spectroscopic transitions (IUPAC Technical Report)

“…Conversely, ab initio spectral shapes calculated by molecular dynamics simulations [61,62] should be reliable at temperatures above the quantum limit and can easily be repeated for many temperatures. So far such studies on water seem to have focused heavily on the room temperature regime [20,[74][75][76]. Extending molecular dynamics simulations to probe the effects of temperature would clearly be very useful.…”

“…We expect the latter to be reliable, in view of the quality of calculations at room temperature. Furthermore, the temperature dependences of Γ 2 and Δ 2 , like Γ and Δ, can be investigated by using semiclassical calculations [74,76].…”