HIGH SENSITIVITY CRDS OF THE $a^{1}\Delta_{g}$$\leftarrow$$X^{3}\Sigma^{-}_{g}$ BAND OF OXYGEN NEAR 1.27 $\mu$m: MAGNETIC DIPOLE AND ELECTRIC QUADRUPOLE TRANSITIONS IN SPECTRA OF FIVE ISOTOPOLOGUES

Author Institution: Universite Joseph Fourier/CNRS, Laboratoire de Spectrometrie Physique, 38402 Saint Martin d'Heres, FRANCE; Harvard-Smithsonian Center for Astrophysics, Atomic and Molecular; Physics Division, Cambridge MA 02138-1516, USA; Universite Joseph Fourier/CNRS, Laboratoire de Spectrometrie Physique, 38402 Saint Martin d'Heres, FRANCEThe knowledge of accurate spectroscopic parameters for the $a^{1}\Delta_{g}$$\leftarrow$$X^{3}\Sigma^{-}_{g}$ band of molecular oxygen near 1.27 $\mu$m 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 Continuous Wave-Cavity Ring Down Spectroscopy (CW-CRDS) technique has been used to record with high sensitivity the absorption spectrum of this band. The spectra were obtained between 7640 and 7917 cm$^{-1}$ with ``natural'' oxygen and with a sample highly enriched in $^{18}$O. The absolute intensities of 377 and 652 oxygen transitions were measured in the two spectra, respectively. They include the $a^{1}\Delta_{g}$$\leftarrow$$X^{3}\Sigma^{-}_{g}$ (0-0) bands of $^{16}$O$_{2}$, $^{16}$O$^{18}$O, $^{16}$O$^{17}$O, $^{17}$O$^{18}$O and $^{18}$O$_{2}$. The (0-0) bands of $^{16}$O$_{2}$ and $^{18}$O$_{2}$ show (previously undetected) electric quadrupole transitions with line intensities ranging from 1$\times$10$^{-30}$ to 1.9$\times$10$^{-28}$ cm/molecule. They are accompanied by the $a^{1}\Delta_{g}$$\leftarrow$$X^{3}\Sigma^{-}_{g}$ (1-1) hot bands which are also reported for the first time. 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