Direct validation of the ab initio quantum-scattering calculations on the accurate experimental spectra of the S(2) 2−0 line of D₂ perturbed by collisions with H₂ molecules (see the main text for details). The black dots are the experimental spectra, and the red lines are the ab initio profiles. Below each profile, we show the absolute residuals of two models: the SDBB profile and the mHT profile. To quantify how well theory agrees with experiments, we report the relative (with respect to the profile peak value) root mean square errors (rRMSEs) of the experiment-theory differences calculated within the ±FWHM range around the line center (see the percentages below the residuals). The mean rRMSEs are also summarized for each of the models (see the numbers on the right side of the figure).