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Other Fits

Line Intensity Fitting

Line intensities can also be fit, which makes sense in three contexts:
  1. Where absolute intensities have been measured and a fit can therefore determine the transition moment.
  2. Relative intensities have been measured of two or more bands, and the relative transition moments are required.
  3. A series of relative intensity measurements have been made, and the population distribution are required.
The essential procedure is the same as for line position fitting, except that the line intensities replace the positions in the observations file. When fitting, the Fit type combo box should be set to "Intensity" or "Fractional Intensity" rather than "Line", and you will want to make sure that only parameters affecting the intensity are floated. (In principle this will be all parameters, but you will normally want to float the transition moments and temperature only.)

Unless measured intensities are particularly precise, I recommend using "Fractional Iintensity". This forces the estimated error for each intensity to be equal to the intensity itself, and is equivalent to errors that are a constant fraction of the measured intensity. This is often a better match for errors in typical intensity measurements than a standard fit, as intensities are often subject to large errors, and the most meaningful fit is often to the trend. The  average error given by these fits should be interpreted as an average fraction of the intensities, so an error of 0.1 should be interpreted as individual transitions fitting on average to 10% of their intensity.

To fit populations set the required levels up as described in Non-Boltzmann Populations; this then provides a parameter for each level of interest in the manifold that can be floated as for other parameters. Again you will normally want to float these population parameters only.

Energy Level fits

This is essentially a special case of a line position fit. To force the observed value in a given line in the input file to be treated as an energy level, rather than a transition frequency, replace J, S and # for the unwanted state with "-" and leave the manifold field blank. It is also possible to force this for a complete file from the Log Window. If HITRAN or JPL line catalog files are used as input, then these have energy level information in them and selecting EUpper or ELower in the log window will cause the state energy to be worked out (using the line position and lowers state energy for EUpper). For other file formats the values given in the file must be the energy level.