Absolute rotational Raman cross sections for N_2, O_2, and CO_2

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Abstract
We present absolute intensities for rotational Raman scattering (RRS) from N2, O2, and CO2, excited at 488.0 and 647.1 nm. The absolute scattering intensity for N2 at 488.0 nm is characterized by its differential cross section for backscattering, summed over Stokes and anti-Stokes bands and over scattered-light polarizations, which we find to be 1.64 × 10−29 cm2/sr ±8%. The ratio of the cross section for O2 to that for N2 at 488.0 nm is 2.61 ± 5%, whereas the corresponding ratio for CO2 to N2 is 10.6 ± 10%. Our values for RRS cross sections relative to the N2 vibrational Raman cross section are in reasonable agreement with corresponding ratios reported recently by Fenner et al. On the other hand, our absolute cross sections are approximately twice as large as those obtained from the results of Fenner et al., but agree closely with values calculated from recent measurements of the depolarization of Rayleigh scattering. Detailed observations of relative rotational-Raman-line intensities at temperatures of 22, 75, and 125 °C are consistent with theoretical predictions.

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