Edge detection

\(E_{0}\) estimation is a crucial step in XAS data analysis. It identifies the absorption edge position, which is essential for aligning spectra and calculating energy-dependent quantities like the photoelectron wavevector. EstraPy provides two commands for this taks:

align: estimates the reference \(E_{0}\), relative to the ref column, and shifts the dataset to align to a target edge energy.
edgeenergy: estimates \(E_{0}\) from the experimental section, relative to the a column. Computes relative energy (e) and wavevector (k).

The two commands share the same estimation logic, based on a customizable chain of processing operations called a method.

Align

The align command calculates the \(E_{0}\) on the ref column, representing \(\alpha_{ref}(E)\), and shifts each spectrum in order to align the file to the correct \(E_{0}\) value for the selected element.

align <method> [--options]

Argument	Explanation
`method`	Defines the method used in the \(E_{0}\) estimation. The method syntax is defined below
`--E0` / `-E` `<energy>`	The tabulated \(E_{0}\) value for the analyzed edge. The energy can be specified either by the value, such as `14652eV`, or as an element edge, such as `Pd.K`. If needed, the tabulated edge can be shifted, e.g. `Pd.K+1.2eV`
`--dE0` / `-d` `<value>`	The range around which to search for the \(E_{0}\).
`--search` / `-s` `<energy>`	The energy around which to search for the \(E_{0}\). If not specified, searches around `--E0`. The energy value follows the same syntax as `--E0`.
`--wplot`	Plots each step of the \(E_{0}\) detection.

EdgeEnergy

The edgeenergy command calculates the \(E_{0}\) on the a column, that is on \(\alpha_{exp}(E)\). Afterwards, the command also calculates the indices e, representing the relative energy from the determined \(E_{0}\) value, and k, representing the wavevector. The k column also contains negative values, as this column is calculated with a symmetrical square root function. This is only for mathematical convenience.

edgeenergy <method> [--options]

Argument	Explanation
`method`	Defines the method used in the \(E_{0}\) estimation. The method syntax is defined below
`--E0` / `-E` `<energy>`	The tabulated \(E_{0}\) value for the analyzed edge. The energy can be specified either by the value, such as `14652eV`, or as an element edge, such as `Pd.K`. If needed, the tabulated edge can be shifted, e.g. `Pd.K+1.2eV`
`--dE0` / `-d` `<value>`	The range around which to search for the \(E_{0}\).
`--wplot`	Plots each step of the \(E_{0}\) detection.

Method

Methods for both commands can be constructed from a series of operations, defined in the table below. The operations must end with a terminal method, which estimates a single number.

Operation	n	Explanation
`c`	✓	Cuts the current data range to the range defined as `E0`-`dE0`~`E0`+`dE0`. If `n` is specified, expands the range by `n`\(\cdot\)`dE0` on both sides to provide a buffer for other operations.
`p`	✓	Performs polynomial regression of order `n` on the current data.
`s`	✓	Smooths the data, with a window of size `n`.
`d`	✓	Calculates the `n`-th derivative of the data.
`i`	✓	Interpolates the data with a spline of order `n`.
`M`	✗	Terminal method, calculates the maximum of the current data.
`m`	✗	Terminal method, calculates the minimum of the current data.
`Z`	✗	Terminal method, calculates the zero of the current data.
`S`	✗	Terminal method, bypasses all instructions and sets the E0 value to the given `E0`.

Alternatively, the method can be one of the following options, which are simply aliases for some common methods.

Alias	Operations
`set`	`S`
`fitderivative`	`c1.s5.d1.p3.M`
`fitpolynomial`	`c1.p3.d1.M`
`fitmaximum`	`c1.p3.M`
`interpderivative`	`c1.s5.d1.i3.M`
`maximum`	`c1.i3.M`