Line shape parameters of self-broadened CO transitions in the (3-0) overtone band

This study employs laser-locked cavity ring-down spectroscopy to investigate 15 weak ¹²C¹⁶O transitions in the near-infrared, corresponding to the P and R branches of the (3-0) band with rotational quantum numbers $J$ ranging from 25 to 35. Most spectra were recorded at low pressures (below 1333 Pa), where Doppler broadening dominates, and collision broadening is mainly driven by speed-dependent interactions. This environment enables precise determination of collisional line shape parameters. The Padé approximation and polynomial fit were used to estimate speed-dependent Voigt (SDV) broadening parameters, extending the data to higher rotational quantum numbers. Accurate self-broadening parameters for CO were obtained, which are essential for studying pressure broadening by other atmospheric gases. These results will support high-precision radiative transfer models for Earth’s atmosphere in this spectral region.