The first observation of the 12C16O2 absorption bands near 660 nm.

[Display omitted] • Bruker IFS 125 HR Fourier transform spectrometer with LED light source and optical path length of about 1 km reaches the sensitivity of 1.23 × 10-10 cm−1 near 660 nm. • First observation of the 3005 i − 00,001 (i = 2,3) and 60031–00001 absorption bands of 12C16O 2 near 660 nm. • Measured line positions and intensities of the 3005 i − 00,001 (i = 2,3) and 60031–00001 bands of 12C16O 2. • HITRAN2020 line parameters for the studied bands should be updated. The absorption spectra of carbon dioxide were recorded in the region from 15,000 to 15,300 cm−1, using a Bruker IFS 125 HR Fourier transform spectrometer and a 30 m multipass cell with the White type optical system. The recording was performed at a spectral resolution of 0.044 – 0.050 cm−1, room temperature, a path length of 1057.95 m and pressures of 185 and 362 mbar. Utilization of a LED as a light source provided a sensitivity (noise equivalent absorption) at the level of k ν = 1.23 × 10-10 cm−1 and allowed detection of a number of lines of two 3005 i − 00001 (i = 2,3) bands and several lines of the 60031 – 00001 band of 12C16O 2 with the intensity values down to 10-30 cm−1/(molecule cm−2) at 296 K. These bands were observed for the first time. The uncertainty of the line position measurements was estimated to be about 0.005 cm−1 for the unblended lines with a high signal-to-noise ratio. The uncertainties of the retrieved line intensities for the strongest unblended lines are at the level of 15 %. The spectroscopic constants for observed bands were fitted to the observed line positions. The vibrational transition dipole moments squared of these bands were fitted to the observed line intensities. The measured line positions were compared to those from the HITRAN2020 database and to those predicted with the global effective Hamiltonian. The measured line intensities were compared to the values from the HITRAN2020 database and from the Ames2021 line list. [ABSTRACT FROM AUTHOR]