Assigning Curve Fit Band Dependencies (Doublets)

There are two types of dependencies you can set up between bands – area ratio and peak separation. Setting up dependencies between these bands allows you to simulate doublets, whereby the parameters of one peak are dependent on another for fitting. The peak that is dependent on another is the secondary peak of the doublet; the independent peak is the primary. Multi-level dependencies are sometimes referred to as multiplets.

Creating a doublet

To create a doublet with a fixed area ratio, first create two bands. Select the band that is to be the dependent (secondary) band, and click the Area button. From the Area Ratio dialog you can choose the independent (primary) band, as well as the ratio. (Use What's This help for further information on the individual fields.) Once you dismiss the dialog, you’ll note that the Ratio column of the dependent band now displays its ratio to the independent band, as well as the index of the independent band. For example, if you selected band 2 and fixed its area to band 1 at 0.5, you would see “1-0.5” in the Ratio field of band 2. This means that band 2 maintains an area 0.5 times that of band 1.

To create a doublet with a fixed peak separation, first create two bands. Select the band that is to be the dependent (secondary) band, and click the Peak button. From the Peak Separation dialog, you can choose the independent (primary) band, as well as the Separation. (Use What's This help for further information on the individual fields.) Once you dismiss the dialog, you’ll note that the Separation column of the dependent band now displays its separation (in eV) relative to the independent band, as well as the index of the independent band. For example, if you selected band 2 and fixed its separation to band 1 at .3, you would see “1-0.3” in the Separation field of band 2. This means that band 2 maintains a position 0.3eV plus that of band 1.

Note that you can create doublets with both area ratio and peak separation locking. Simply select an existing dependent band from the list and choose the desired dependency.

Removing a doublet

To remove a doublet dependency, select a dependent band and click either Area or Peak. Choose remove to remove that dependency. If a band has both an Area and Peak dependency, you must remove the dependencies individually.

How doublets affect estimates

The dependencies used to simulate doublets follow some rules as to behavior when adjusting limits manually and when fitting.

Area Ratio:

a) Adjusting any parameter of the independent band (with the exception of position) causes the corresponding parameter of the dependent band to adjust in order to maintain the selected ratio.

b) Adjusting any parameter of the dependent band except for position and intensity causes the intensity to adjust in order to maintain the selected ratio.

c) Adjusting the intensity of the dependent band causes the FWHM to adjust in order to maintain the selected ratio.

d) Adjusting the position of the either band does nothing.

In general, note that whatever parameters are adjusted in either the dependent or independent band, the area ratio is maintained.

Peak Separation

a) Adjusting the position of the independent band causes the position of the dependent band to adjust in order to maintain the selected peak separation.

b) Adjusting the position of the dependent band causes the peak separation to change.

Adjusting Individual Curve Fit Band Limits, Invariance, and Locking

Additional Curve Fitting Topics