Absorption cross sections and line shape for the NO3(0–0) band

The absorption cross section of the nitrate free radical has been scanned by a tunable dye laser with 0.05 nm resolution (FWHM) between 613 and 672 nm, and portions of the region were scanned at high resolution (200 MHz) with the laser in single-frequency mode. These data, combined with other recent measurements, give a peak cross section at 661.9 nm of 1.90×10−17 cm2; and the integrated cross section over the 0–0 band from 14 910 to 15 290 cm−1 is 2.02×10−15 cm. Two recent studies that were said to disagree because of different peak cross sections are shown to agree in terms of integrated absorption cross section over the 0–0 band. It is confirmed that the spectrum is diffuse even under very high resolution. The 0–0 band is well approximated by two closely spaced Lorentzian functions.