High Sensitivity CRDS of the a1Δg X3Σg Band of Oxygen near 1.27 μ: Magnetic Dipole and Electric Quadrupole Transitions in Different Bands of Six Isotopologues

The knowledge of accurate spectroscopic parameters for a1Δg X3Σ− g band of molecular oxygen near 1.27 μ is very important in the field of remote sensing. Although, this band was studied by spectroscopists for over a century a lot of discrepancies still remain in the previously reported line positions and intensities. In this work the CWCavity Ring Down Spectroscopy (CW-CRDS) technique has been used to record the high sensitivity absorption spectrum of this band. The spectra were obtained between 7640 and 7917 cm−1 with “natural” oxygen and with samples highly enriched in 18O and 17O. They measured transitions belong to the a1Δg X3Σ− g (0-0) bands of 16O2, 16O18O, 16O17O, 17O18O, 18O2 and 17O2. The (0-0) bands of 16O2 and 18O2 show (previously undetected) electric quadrupole transitions with line intensities ranging from 1X10−30 to 1.9X10−28 cm/molecule. They are accompanied by the a1Δg X3Σ− g (1-1) hot bands which are also reported for the first time. Lines of the isotopologues containing 17O atom were observed to be plagued with unresolved hyperfine structure, especially in the 17O2 spectrum. Accurate spectroscopic parameters for the observed bands were derived from a global fit of the experimental line positions, combined with microwave and Raman measurements available in the literature.