High-sensitivity CW-cavity ringdown spectroscopy of 12CO2 near 1.5 μm

The absorption spectrum of carbon dioxide in natural isotopic abundance has been recorded by CW-cavity ringdown spectroscopy with a setup based on fibered DFB lasers. By using a series of 31 DFB lasers, the CO2 spectrum could be recorded in the 6132-6747 cm−1 region with a typical sensitivity of 5 × 10−10 cm−1. More than 3300 line positions were measured and assigned to the 12C16O2 species while only 1159 (generally calculated) line positions are provided by the HITRAN database. Altogether, the band-by-band analysis has led to the determination of the rovibrational parameters of 53, 5, and 9 bands for the 12C16O2, 16O12C17O, and 16O12C18O isotopologues, respectively. For the three studied isotopologues, the majority of the observed line positions show an agreement close to the experimental uncertainty (3 × 10−3 cm−1) with the predictions of their respective effective Hamiltonian models. Maximum deviations of the order of 0.03, 0.05, and 0.04 cm−1 were, however, evidenced for 12C16O2, 16O12C17O, and 16O12C18O, respectively. As some observed line positions show significant deviations from the predictions of the effective Hamiltonian model and as the observed data set has been recently enlarged by newly reported measurements, the observed line positions were gathered with all the data available in the literature in order to refine the set of effective Hamiltonian parameters of the 12C16O2 isotopic species. The refined set of 130 effective Hamiltonian parameters reproduces more than 29 000 observed line positions of 12C16O2 with an RMS = 0.002 cm−1. The comparison of our line positions values with those published earlier and with the line list provided by HITRAN is discussed.