Comparison of line intensities in the ν₅ band of C₂H₂ between HITRAN data (blue) and the present calculations using TOPSEGI (red). The top panel shows the full simulated band profile in terms of line intensity versus wavenumber, illustrating overall agreement in line positions and relative strengths. The bottom three panels display the relative intensity errors as a function of rotational quantum number J_l in the P, Q, and R branches, respectively. The deviation increases toward high-J_l lines, but this is consistent with limitations in the HITRAN reference intensities and the harmonic dipole approximation used in the present model. Here, the vertical lines identify the highest-J_l observed, with corresponding deviations reaching up to approximately 2%.