Knowledge Bank

Over the last decade we have analysed hundreds of infrared molecular absorption spectra with an interactive nonlinear least squares spectrum fitting technique. Spectra have been analysed separately, and parameters such as the line: intensity have been determined by combining the results from the individual fittings. Recently, we have developed an improved analyses proceedure which allows the simultaneous fitting of multiple spectra. In this ``global fitting” approach, spectroscopic and instrumental parameters are determined with improved accuracy as a consequence of the more rigorous solution of the problem. For example, the multiple spectrum fitting technique determines the values of correlated parameters better than averaging values determined by fitting the spectra separately. Parameter errors and the correlations among the retrieved parameters are explicitly calculated in our new procedure. A flexible interface (either batch or interactive) has been developed for specifying the fitting of any combination of the following parameters: {\bf Instrumental} (each spectrum): polynomial fit to continuum level; zero level; amplitude, period and phase of channel spectra; electronic time constant for tunable diode laser spectra; resolution and/or phase error for Fourier transform spectrometer data. {\bf Spectroscopic} (each spectral line): position, pressure shift, temperature dependence of the pressure shift, intensity, Lorentz halfwidth, temperature dependence of the Lorentz halfwidth, Doppler width, pressure narrowing and line mixing.