Knowledge Bank

The multispectrum nonlinear least squares fitting technique described by Benner $etal.1$ has been applied to air and nitrogen broadened spectra of methane in the 2 to $4\mu m$ spectral region obtained with the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory. Problems fitting the methane spectra one at a $time2$ have been investigated with the multispectrum fitting approach yielding new information about the lineshape below the resolution of the spectrometer. The list of effects now included in the fitting are: Input Parameters. Each spectrum: Pressure, path length and temperature for each of up to 3 paths; mixing ratio for up to 3 gases for each path; apodization function; maximum path difference of FTS; solid angle of FTS entrance aperture. Each spectral line: Gas and Isotope Solvable Parameters. Each spectrum: Second order polynomial fit to continuum; zero level; resolution; period, phase and amplitude for up to 10 channel spectra; diode laser electronic time constant; FTS phase error, period, phase and amplitude of periodic source variations. Each spectral line: Zero pressure position; intensity; lower state energy; self and foreign gas Lorentz broadening; temperature dependence of self and foreign gas Lorentz broadening; self and foreign gas induced pressure shifts; temperature dependence of self and foreign gas induced pressure shifts (2 models); Doppler width; collisional narrowing; line mixing.