Re-evaluation of ortho-para-dependence of self-pressure broadening in the $v_1+v_3$ band of acetylene.

Measurements of self-pressure broadened line profiles of the R(8)$-$R(13) lines in the $v_1+v_3$ band of acetylene near 1.52$\mu$m are reported. The data were analyzed using a variety of line profile models ranging from a simple Voigt convolution of Gaussian and Lorentzian components to a complete implementation of the Hartmann-Tran profile (HTP). No evidence was found for a, previously reported [Iwakuni et al. \textit{Phys. Rev. Letts.} \textbf{117}, 143902(5) 2016], systematic alternation in self-pressure broadened line widths with the nuclear spin state of the molecule. Analysis of the data brought out the need for a careful accounting of weak background absorptions due to hot-band and lower abundance isotopomer lines as well as the requirement for the use of an accurate line profile model. The data were adequately fit using the quadratic speed-dependent Voigt profile model, and parameters describing the average and speed dependent broadening and shift, and line strengths were determined for each line. Smaller contributions to the full HTP including the rate of velocity-changing collisions and the correlation between velocity- and state-changing collisions were only marginally determined and did not significantly improve the overall quality of the line profile fitting.