Pre-edge Correction

The preedge command removes the pre-edge background from the absorption signal and determines the absorption edge energy (\(E_0\)).

Basic Usage 

preedge <range> [options]

Fit a polynomial to the absorption signal before the edge and subtract it to establish a zero baseline.

Examples:

preedge .. -50eV --linear

preedge 8000eV 8300eV --degree 1

Command options

Option Description
<range> Energy range for fitting the pre-edge polynomial (required). See range for details.

Polynomial degree options

These options specify the degree of the polynomial used to fit the pre-edge background, and are mutually exclusive.

Option Description
--degree <n>
--deg <n>		 Polynomial degree (default: 1)
--constant
-C		 Use constant (degree 0)
--linear
-l		 Use linear fit (degree 1, default)
--quadratic
-q		 Use quadratic fit (degree 2)
--cubic
-c		 Use cubic fit (degree 3)

Results

The command subtracts the extrapolated fitted polynomial from the absorption signal, and updates the a column with the corrected absorption. It also defines the pre column, containing the fitted polynomial values.

Tips and Best Practices

  1. Range selection:
    • Start as far from the edge as your data allows
    • End 20-100 eV before the edge
    • Avoid including any XANES features
  2. Polynomial degree:
    • Linear (degree 1) works for most cases
    • Use constant (degree 0) only if baseline is flat
    • Use quadratic (degree 2) for strongly curved backgrounds
    • Avoid higher degrees unless absolutely necessary

See also: