X-ray notation

X-ray notation is a method of labeling atomic orbitals that grew out of X-ray science. Also known as IUPAC notation, it was adopted by the International Union of Pure and Applied Chemistry in 1991 as a simplification of the older Siegbahn notation.^[1] In X-ray notation, every principal quantum number is given a letter associated with it. In many areas of physics and chemistry, atomic orbitals are described with spectroscopic notation (1s, 2s, 2p, 3s, 3p, etc.), but the more traditional X-ray notation is still used with most X-ray spectroscopy techniques including AES and XPS.

Conversion^[2][3]

Quantum numbers				Atomic notation	X-ray notation
n {\displaystyle n}	ℓ {\displaystyle \ell }	s {\displaystyle s}	j {\displaystyle j}
1	0	1/2	1/2	1s1/2	K1
2	0	1/2	1/2	2s1/2	L1
2	1	1/2	1/2	2p1/2	L2
2	1	1/2	3/2	2p3/2	L3
3	0	1/2	1/2	3s1/2	M1
3	1	1/2	1/2	3p1/2	M2
3	1	1/2	3/2	3p3/2	M3
3	2	1/2	3/2	3d3/2	M4
3	2	1/2	5/2	3d5/2	M5
4	0	1/2	1/2	4s1/2	N1
4	1	1/2	1/2	4p1/2	N2
4	1	1/2	3/2	4p3/2	N3
4	2	1/2	3/2	4d3/2	N4
4	2	1/2	5/2	4d5/2	N5
4	3	1/2	5/2	4f5/2	N6
4	3	1/2	7/2	4f7/2	N7

• X-ray sources are classified by the type of material and orbital used to generate them. For example, Cu_Kα X-rays are emitted from the K orbital of copper.
• X-ray absorption is reported as which orbital absorbed the x-ray photon. In EXAFS and XMCD the L-edge or the L absorption edge is the point where the L orbital begins to absorb x-rays.
• Auger peaks are identified with three orbital definitions, for example KL₁L₂. In this case, K represents the hole that is initially present at the core level, L₁ the initial state of the electron that relaxes down into the core level hole, and L₂ the initial energy state of the emitted electron.

• Siegbahn notation for the names of spectral lines used in X-ray spectroscopy
• Spectroscopic notation
• Term symbol notation