Knowledge Bank

The $\nu 3$ band of methane is important for studies of the Earth’s atmosphere both because of its strength (so that small amounts of methane can be detected remotely) and due to its interference in the detection of other gases such as HCI which absorb in the same spectral region. The P and R branch manifolds in this band are more compact than other strong methane bands and the effects of line mixing are apparent. The effects of line mixing are, however, difficult to sort out from Lorentz broadening and line shifts when analyzing laboratory spectra. With our multispectrum nonlinear least squares fitting technique these effects are better separated from one another. Improved characterization of this band using spectra from interferometers of the National Solar Observatory and Universite de Parris-Sud has been attained for air and self broadening. The results require that there be either mixing between lines of different species (A, E, or F) or else between manifolds (which are about $10cm-1$ apart.)