The pressure effect on the line profiles observed in the ν1+ν3 band of acetylene: Revisited

In our previous paper [K. Iwakuni et al., Phys. Rev. Lett. 117, 1439026 (2018)] the ortho-para dependence of the pressure effects was reported for the ν1+ν3 band of acetylene measured by dual-comb spectroscopy. Sears and coworkers (Gross et al., 2021) reevaluated the profile parameters for some lines of this band by comb-referenced laser spectroscopy, and pointed out that the ortho-para phenomenon must be a consequence of the use of Voigt function as the profile function, with the Doppler widths fixed at their theoretical values. Thus, we have remeasured this band with two improved spectrometers, the comb-locked laser spectrometer of the National Metrology Institute of Japan and another dual-comb spectrometer of Yokohama National University, and analyzed the lines by using the speed-dependent Voigt function as the profile function with several options. By the present work, we confirm the fact pointed out by Sears and coworkers, and present some remaining problems in the experimental determination of the line profile parameters.