diff --git a/base_classes/NXedge.nxdl.xml b/base_classes/NXedge.nxdl.xml
index 6f9a752cab..ef8a3e61ae 100644
--- a/base_classes/NXedge.nxdl.xml
+++ b/base_classes/NXedge.nxdl.xml
@@ -24,10 +24,82 @@
- Absorption edge
+
+ An absorption edge is a sharp discontinuity in the X-ray absorption spectrum
+ of an element that occurs when the incident photon energy equals the binding
+ energy of a core electron, enabling photoionization of that shell.
+
- Name of the edge
+ Name of the absorption edge specified using
+ `IUPAC notation`_ (e.g., ``K``, ``L2``, ``M5``), which identifies the
+ shell and sub-shell from which the electron is ejected.
+
+ Correspondence between IUPAC and electronic level notations:
+
+ .. list-table::
+ :header-rows: 1
+
+ * - IUPAC
+ - Electronic level
+ * - K
+ - 1s
+ * - L1
+ - 2s
+ * - L2
+ - :math:`2p_{1/2}`
+ * - L3
+ - :math:`2p_{3/2}`
+ * - M1
+ - 3s
+ * - M2
+ - :math:`3p_{1/2}`
+ * - M3
+ - :math:`3p_{3/2}`
+ * - M4
+ - :math:`3d_{3/2}`
+ * - M5
+ - :math:`3d_{5/2}`
+ * - N1
+ - 4s
+ * - N2
+ - :math:`4p_{1/2}`
+ * - N3
+ - :math:`4p_{3/2}`
+ * - N4
+ - :math:`4d_{3/2}`
+ * - N5
+ - :math:`4d_{5/2}`
+ * - N6
+ - :math:`4f_{5/2}`
+ * - N7
+ - :math:`4f_{7/2}`
+ * - O1
+ - 5s
+ * - O2
+ - :math:`5p_{1/2}`
+ * - O3
+ - :math:`5p_{3/2}`
+ * - O4
+ - :math:`5d_{3/2}`
+ * - O5
+ - :math:`5d_{5/2}`
+ * - O6
+ - :math:`5f_{5/2}`
+ * - O7
+ - :math:`5f_{7/2}`
+ * - P1
+ - 6s
+ * - P2
+ - :math:`6p_{1/2}`
+ * - P3
+ - :math:`6p_{3/2}`
+ * - P4
+ - :math:`6d_{3/2}`
+ * - P5
+ - :math:`6d_{5/2}`
+
+ .. _IUPAC notation: https://doi.org/10.1002/xrs.1300200308
@@ -49,10 +121,20 @@
+
+
+
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+
+
-
+
+
+
+ Energy of the absorption edge.
+
diff --git a/base_classes/NXemission_line.nxdl.xml b/base_classes/NXemission_line.nxdl.xml
new file mode 100644
index 0000000000..12c11aa89f
--- /dev/null
+++ b/base_classes/NXemission_line.nxdl.xml
@@ -0,0 +1,626 @@
+
+
+
+
+
+ An emission line is a spectral line with a discrete frequency that is
+ characteristic of the emitting atom.
+
+
+
+ The emission line name using either the `IUPAC notation`_, i.e. initial and final
+ edge separated by a hyphen (e.g. ``K-L3``), or the Latinized Siegbahn
+ notation (e.g. ``Ka1``).
+
+ Correspondence between IUPAC and Siegbahn notations:
+
+ .. list-table::
+ :header-rows: 1
+
+ * - IUPAC
+ - Siegbahn
+ - Latinized Siegbahn
+ * - K-L3
+ - :math:`K\alpha_1`
+ - Ka1
+ * - K-L2
+ - :math:`K\alpha_2`
+ - Ka2
+ * - K-L1
+ - :math:`K\alpha_3`
+ - Ka3
+ * - K-M3
+ - :math:`K\beta_1`
+ - Kb1
+ * - K-N3
+ - :math:`K\beta_2'`
+ - Kb2\'
+ * - K-N2
+ - :math:`K\beta_2''`
+ - Kb2\'\'
+ * - K-M2
+ - :math:`K\beta_3`
+ - Kb3
+ * - K-N5
+ - :math:`K\beta_4'`
+ - Kb4\'
+ * - K-N4
+ - :math:`K\beta_4''`
+ - Kb4\'\'
+ * - K-N4
+ - :math:`K\beta_{4x}`
+ - Kb4x
+ * - K-M5
+ - :math:`K\beta_5'`
+ - Kb5\'
+ * - K-M4
+ - :math:`K\beta_5''`
+ - Kb5\'\'
+ * - L3-M5
+ - :math:`L\alpha_1`
+ - La1
+ * - L3-M4
+ - :math:`L\alpha_2`
+ - La2
+ * - L2-M4
+ - :math:`L\beta_1`
+ - Lb1
+ * - L3-N5
+ - :math:`L\beta_2`
+ - Lb2
+ * - L1-M3
+ - :math:`L\beta_3`
+ - Lb3
+ * - L1-M2
+ - :math:`L\beta_4`
+ - Lb4
+ * - L3-O4,5
+ - :math:`L\beta_5`
+ - Lb5
+ * - L3-N1
+ - :math:`L\beta_6`
+ - Lb6
+ * - L3-O1
+ - :math:`L\beta_7`
+ - Lb7
+ * - L3-N6,7
+ - :math:`L\beta_7'`
+ - Lb7\'
+ * - L1-M5
+ - :math:`L\beta_9`
+ - Lb9
+ * - L1-M4
+ - :math:`L\beta_{10}`
+ - Lb10
+ * - L3-N4
+ - :math:`L\beta_{15}`
+ - Lb15
+ * - L2-M3
+ - :math:`L\beta_{17}`
+ - Lb17
+ * - L2-N4
+ - :math:`L\gamma_1`
+ - Lg1
+ * - L1-N2
+ - :math:`L\gamma_2`
+ - Lg2
+ * - L1-N3
+ - :math:`L\gamma_3`
+ - Lg3
+ * - L1-O3
+ - :math:`L\gamma_4`
+ - Lg4
+ * - L1-O2
+ - :math:`L\gamma_4'`
+ - Lg4\'
+ * - L2-N1
+ - :math:`L\gamma_5`
+ - Lg5
+ * - L2-O4
+ - :math:`L\gamma_6`
+ - Lg6
+ * - L2-O1
+ - :math:`L\gamma_8`
+ - Lg8
+ * - L2-N6,7
+ - :math:`L\gamma_8'`
+ - Lg8\'
+ * - L2-M1
+ - :math:`L\eta`
+ - Ln
+ * - L3-M1
+ - :math:`Ll`
+ - Ll
+ * - L3-M3
+ - :math:`Ls`
+ - Ls
+ * - L3-M2
+ - :math:`Lt`
+ - Lt
+ * - L3-N6,7
+ - :math:`Lu`
+ - Lu
+ * - L2-N6,7
+ - :math:`Lv`
+ - Lv
+ * - M5-N7
+ - :math:`M\alpha_1`
+ - Ma1
+ * - M5-N6
+ - :math:`M\alpha_2`
+ - Ma2
+ * - M4-N6
+ - :math:`M\beta`
+ - Mb
+ * - M3-N5
+ - :math:`M\gamma`
+ - Mg
+ * - M4,5-N2,3
+ - :math:`M\zeta`
+ - Mz
+
+ .. _IUPAC notation: https://doi.org/10.1002/xrs.1300200308
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+ Energy of the emission line.
+
+
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diff --git a/base_classes/NXemission_lines.nxdl.xml b/base_classes/NXemission_lines.nxdl.xml
deleted file mode 100644
index 395ecb2ed3..0000000000
--- a/base_classes/NXemission_lines.nxdl.xml
+++ /dev/null
@@ -1,46 +0,0 @@
-
-
-
-
- Emission lines
-
-
- The emission lines are writen using the IUPAC notation, i.e. an
- initial and final edge seprated by a hyphen.
-
- TODO: Extend the enumeration to include all possible emission lines.
-
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diff --git a/base_classes/NXxas_mode.nxdl.xml b/base_classes/NXxas_mode.nxdl.xml
index 12d1fd63bb..02da979ea5 100644
--- a/base_classes/NXxas_mode.nxdl.xml
+++ b/base_classes/NXxas_mode.nxdl.xml
@@ -135,7 +135,11 @@
-
+
+
+ Collection of emission lines detected or used in this measurement.
+
+