No constraints have been applied and the result is a reasonable fit to the experimental data but the fitting parameters are not readily open to chemical interpretation. For example, the FWHM are much bigger than would typically be expected from C 1s profiles the given instrumental resolution. An initial fit to the C 1s spectra shown in Figure 1. The PAA stoichiometry is still doubtful but the essential positions for a pure PAA envelope have more or less appeared.
Further input is required to make sense of the new synthetic model.
To constraint a parameter so that it does not adjust during an optimization step, set the constraint interval to have the same value as the fixed value. E.g., if it is required to set the FWHM value to 1.1, the constraint interval should be entered with the value 1.1,1.1 . Actually, it is sufficient to set the parameter value outside the constraint range currently defined for the parameter. Figure 4 is an example of such data where a set of three line-shapes has been used to model the clean PAA C 1s data envelope. The important feature is that the stoichiometry and chemical shifts for the C 1s lines can be incorporated into the model and this information is then transferable to other polymer spectra.