Spontaneous Raman scattering by ground-state oxygen atoms

We report the first known observation of Raman scattering by oxygen atoms. The (3)P(2)?(3)P(1) and (3)P(2)?(3)P(0) transitions in the electronic ground state that produced Raman shifts of 158 and 227 cm(-1) were detected. These transitions were observed in a fuel-lean atmospheric H(2) + O(2) flame. By comparing the O electronic and O(2) pure-rotational Raman-scattering intensities, we measured the polarized cross sections for the two lines to be 6 +/- 1 x 10(-31) and 4 +/- 1 x 10(-31) cm(2)/sr, respectively, with an excitation source at 532.1 nm. These cross sections are two to three times stronger than those predicted by a single-configuration single-excitation Coulomb approximation.