Term symbol

In quantum mechanics, the term symbol is an abbreviated description of the (total) angular momentum quantum numbers in a multi-electron atom (however, even a single electron can be described by a term symbol). Each energy level of an atom with a given electron configuration is described by not only the electron configuration but also its own term symbol, as the energy level also depends on the total angular momentum including spin. The usual atomic term symbols assume LS coupling (also known as Russell-Saunders coupling or spin-orbit coupling). The ground state term symbol is predicted by Hund's rules.

The use of the word term for an energy level is based on the Rydberg-Ritz combination principle, an empirical observation that the wavenumbers of spectral lines can be expressed as the difference of two terms. This was later explained by the Bohr quantum theory, which identified the terms (multiplied by hc, where h is the Planck constant and c the speed of light) with quantized energy levels and the spectral wavenumbers (again multiplied by hc) with photon energies.

Tables of atomic energy levels identified by their term symbols have been compiled by the National Institute of Standards and Technology. In this database, neutral atoms are identified as I, singly ionized atoms as II, etc.^[1] Neutral atoms of the chemical elements have the same term symbol for each column in the s-block and p-block elements, but may differ in d-block and f-block elements, if the ground state electron configuration changes within a column. Ground state term symbols for chemical elements are given below.

LS coupling and symbol

For light atoms, the spin-orbit interaction (or coupling) is small so that the total orbital angular momentum L and total spin S are good quantum numbers. The interaction between L and S is known as LS coupling, Russell-Saunders coupling or Spin-Orbit coupling. Atomic states are then well described by term symbols of the form

^2S+1L_J

where

S is the total spin quantum number. 2S + 1 is the spin multiplicity, which represents the number of possible states of J for a given L and S, provided that L ≥ S. (If L < S, the maximum number of possible J is 2L + 1).^[2] This is easily proved by using J_max = L + S and J_min = |L - S|, so that the number of possible J with given L and S is simply J_max - J_min + 1 as J varies in unit steps.

J is the total angular momentum quantum number.

L is the total orbital quantum number in spectroscopic notation. The first 17 symbols of L are:

L =	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	...
	S	P	D	F	G	H	I	K	L	M	N	O	Q	R	T	U	V	(continued alphabetically)^{[note 1]}

The nomenclature (S, P, D, F) is derived from the characteristics of the spectroscopic lines corresponding to (s, p, d, f) orbitals: sharp, principal, diffuse, and fundamental; the rest being named in alphabetical order, except that J is omitted. When used to describe electron states in an atom, the term symbol usually follows the electron configuration. For example, one low-lying energy level of the carbon atom state is written as 1s²2s²2p^2 3P₂. The superscript 3 indicates that the spin state is a triplet, and therefore S = 1 (2S + 1 = 3), the P is spectroscopic notation for L = 1, and the subscript 2 is the value of J. Using the same notation, the ground state of carbon is 1s²2s²2p^2 3P₀.^[1]

Terms, levels, and states

The term symbol is also used to describe compound systems such as mesons or atomic nuclei, or molecules (see molecular term symbol). For molecules, Greek letters are used to designate the component of orbital angular momenta along the molecular axis.

For a given electron configuration

The combination of an S value and an L value is called a term, and has a statistical weight (i.e., number of possible microstates) equal to (2S+1)(2L+1);
A combination of S, L and J is called a level. A given level has a statistical weight of (2J+1), which is the number of possible microstates associated with this level in the corresponding term;
A combination of S, L, J and M_J determines a single state.

The product (2S+1)(2L+1) as a number of possible microstates $|S,m_{S},L,m_{L}\rangle$ with given S and L is also a number of basis states in the uncoupled representation, where S, m_S, L, m_L (m_S and m_L are z-axis components of total spin and total orbital angular momentum respectively) are good quantum numbers whose corresponding operators mutually commute. With given S and L, the eigenstates $|S,m_{S},L,m_{L}\rangle$ in this representation span function space of dimension (2S+1)(2L+1), as $m_{S}=S,S-1,...,-S+1,-S$ and $m_{L}=L,L-1,...,-L+1,-L$ . In the coupled representation where total angular momentum (spin + orbital) is treated, the associated microstates (or eigenstates) are $|J,M_{J},S,L\rangle$ and these states span the function space with dimension of $\sum _{J=J_{min}=|L-S|}^{J_{max}=L+S}(2J+1)$ as $m_{J}=J,J-1,...-J+1,-J$ . Obviously the dimension of function space in both representation must be the same.

As an example, for S = 1, L = 2, there are (2×1+1)(2×2+1) = 15 different microstates (= eigenstates in the uncoupled representation) corresponding to the ³D term, of which (2×3+1) = 7 belong to the ³D₃ (J = 3) level. The sum of (2J+1) for all levels in the same term equals (2S+1)(2L+1) as the dimensions of both representations must be equal as described above. In this case, J can be 1, 2, or 3, so 3 + 5 + 7 = 15.

Term symbol parity

The parity of a term symbol is calculated as

P=(-1)^{\sum_i l_i}\ ,\!

where l_i is the orbital quantum number for each electron. $P=1$ means even parity while $P=-1$ is for odd parity. In fact, only electrons in odd orbitals (with l odd) contribute to the total parity: an odd number of electrons in odd orbitals (those with an odd l such as in p, f,...) correspond to an odd term symbol, while an even number of electrons in odd orbitals correspond to an even term symbol. The number of electrons in even orbitals is irrelevant as any sum of even numbers is even. For any closed subshell, the number of electrons is 2(2l+1) which is even, so the summation of l_i in closed subshells is always an even number. The summation of quantum numbers $\sum _{i}l_{i}$ over open (unfilled) subshells of odd orbitals (l odd) determines the parity of the term symbol. If the number of electrons in this reduced summation is odd (even) then the parity is also odd (even).

When it is odd, the parity of the term symbol is indicated by a superscript letter "o", otherwise it is omitted:

²P^o
_½ has odd parity, but ³P₀ has even parity.

Alternatively, parity may be indicated with a subscript letter "g" or "u", standing for gerade (German for "even") or ungerade ("odd"):

²P_½,u for odd parity, and ³P_0,g for even.

Ground state term symbol

It is relatively easy to calculate the term symbol for the ground state of an atom using Hund's rules. It corresponds with a state with maximum S and L.

Start with the most stable electron configuration. Full shells and subshells do not contribute to the overall angular momentum, so they are discarded.
- If all shells and subshells are full then the term symbol is ¹S₀.
Distribute the electrons in the available orbitals, following the Pauli exclusion principle. First, fill the orbitals with highest m_l value with one electron each, and assign a maximal m_s to them (i.e. +½). Once all orbitals in a subshell have one electron, add a second one (following the same order), assigning m_s = −½ to them.
The overall S is calculated by adding the m_s values for each electron. According to Hund's first rule, the ground state has all unpaired electron spins parallel with the same value of m_s, conventionally chosen as +½. The overall S is then ½ times the number of unpaired electrons. The overall L is calculated by adding the m_l values for each electron (so if there are two electrons in the same orbital, add twice that orbital's m_l).
Calculate J as
- if less than half of the subshell is occupied, take the minimum value J = |L − S|;
- if more than half-filled, take the maximum value J = L + S;
- if the subshell is half-filled, then L will be 0, so J = S.

As an example, in the case of fluorine, the electronic configuration is 1s²2s²2p⁵.

1. Discard the full subshells and keep the 2p⁵ part. So there are five electrons to place in subshell p (l = 1).

2. There are three orbitals (m_l = 1, 0, −1) that can hold up to 2(2l + 1) = 6 electrons. The first three electrons can take m_s = ½ (↑) but the Pauli exclusion principle forces the next two to have m_s = −½ (↓) because they go to already occupied orbitals.

	m_l
	+1	0	−1
m_s:	↑↓	↑↓	↑

3. S = ½ + ½ + ½ − ½ − ½ = ½; and L = 1 + 0 − 1 + 1 + 0 = 1, which is "P" in spectroscopic notation.

4. As fluorine 2p subshell is more than half filled, J = L + S = ³⁄₂. Its ground state term symbol is then ^2S+1L_J = ²P_³⁄₂.

Atomic term symbols of the chemical elements

In the periodic table, because atoms of elements in a column usually have the same outer electron structure, and always have the same electron structure in the "s-block" and "p-block" elements (see block (periodic table)), all elements may share the same ground state term symbol for the column. Thus, hydrogen and the alkali metals are all ²S_¹⁄₂, the alkali earth metals are ¹S₀, the boron column elements are ²P_¹⁄₂, the carbon column elements are ³P₀, the pnictogens are ⁴S_³⁄₂, the chalcogens are ³P₂, the halogens are ²P_³⁄₂, and the inert gases are ¹S₀, per the rule for full shells and subshells stated above.

Term symbols for the ground states of all chemical elements are given in the collapsed table below (with citations here). In the d-block and f-block, the term symbols are not always the same for elements in the same column of the periodic table.

Element			Group	Electron configuration	Term symbol
					^{1, 2,}	S, P,
1	H	hydrogen	1	1s¹	²S_¹⁄₂	S²S_¹⁄₂
2	He	helium	18	1s²	¹S₀	S¹S₀
3	Li	lithium	1	[He] 2s¹	²S_¹⁄₂	S²S_¹⁄₂
4	Be	beryllium	2	[He] 2s²	¹S₀	S¹S₀
5	B	boron	13	[He] 2s² 2p¹	²P_¹⁄₂	P²P_¹⁄₂
6	C	carbon	14	[He] 2s² 2p²	³P₀	P³P₀
7	N	nitrogen	15	[He] 2s² 2p³	⁴S_³⁄₂	S⁴S_³⁄₂
8	O	oxygen	16	[He] 2s² 2p⁴	³P₂	P³P₂
9	F	fluorine	17	[He] 2s² 2p⁵^[3]	²P_³⁄₂	P²P_³⁄₂
10	Ne	neon	18	[He] 2s² 2p⁶	¹S₀	S¹S₀
11	Na	sodium	1	[Ne] 3s¹	²S_¹⁄₂	S²S_¹⁄₂
12	Mg	magnesium	2	[Ne] 3s²	¹S₀	S¹S₀
13	Al	aluminium	13	[Ne] 3s² 3p¹	²P_¹⁄₂	P²P_¹⁄₂
14	Si	silicon	14	[Ne] 3s² 3p²	³P₀	P³P₀
15	P	phosphorus	15	[Ne] 3s² 3p³	⁴S_³⁄₂	S⁴S_³⁄₂
16	S	sulfur	16	[Ne] 3s² 3p⁴	³P₂	P³P₂
17	Cl	chlorine	17	[Ne] 3s² 3p⁵	²P_³⁄₂	P²P_³⁄₂
18	Ar	argon	18	[Ne] 3s² 3p⁶	¹S₀	S¹S₀
19	K	potassium	1	[Ar] 4s¹	²S_¹⁄₂	S²S_¹⁄₂
20	Ca	calcium	2	[Ar] 4s²	¹S₀	S¹S₀
21	Sc	scandium	3	[Ar] 3d¹ 4s²	²D_3/2	D²D_3/2
22	Ti	titanium	4	[Ar] 3d² 4s²	³F₂	F³F₂
23	V	vanadium	5	[Ar] 3d³ 4s²	⁴F_3/2	F⁴F_3/2
24	Cr	chromium	6	[Ar] 3d⁵ 4s¹	⁷S₃	S⁷S₃
25	Mn	manganese	7	[Ar] 3d⁵ 4s²	⁶S_5/2	S⁶S_5/2
26	Fe	iron	8	[Ar] 3d⁶ 4s²	⁵D₄	D⁵D₄
27	Co	cobalt	9	[Ar] 3d⁷ 4s²	⁴F_9/2	F⁴F_9/2
28	Ni	nickel	10	[Ar] 3d⁸ 4s² or [Ar] 3d⁹ 4s¹	³F₄	F³F₄
29	Cu	copper	11	[Ar] 3d¹⁰ 4s¹	²D_1/2	D²D_1/2
30	Zn	zinc	12	[Ar] 3d¹⁰ 4s²	¹S₀	S¹S₀
31	Ga	gallium	13	[Ar] 3d¹⁰ 4s² 4p¹	²P_¹⁄₂	P²P_¹⁄₂
32	Ge	germanium	14	[Ar] 3d¹⁰ 4s² 4p²	³P₀	P³P₀
33	As	arsenic	15	[Ar] 3d¹⁰ 4s² 4p³	⁴S_³⁄₂	S⁴S_³⁄₂
34	Se	selenium	16	[Ar] 3d¹⁰ 4s² 4p⁴	³P₂	P³P₂
35	Br	bromine	17	[Ar] 3d¹⁰ 4s² 4p⁵	²P_³⁄₂	P²P_³⁄₂
36	Kr	krypton	18	[Ar] 3d¹⁰ 4s² 4p⁶	¹S₀	S¹S₀
37	Rb	rubidium	1	[Kr] 5s¹	²S_¹⁄₂	S²S_¹⁄₂
38	Sr	strontium	2	[Kr] 5s²	¹S₀	S¹S₀
39	Y	yttrium	3	[Kr] 4d¹ 5s²	²D_3/2	D²D_3/2
40	Zr	zirconium	4	[Kr] 4d² 5s²	³F₂	F³F₂
41	Nb	niobium	5	[Kr] 4d⁴ 5s¹	⁶D_1/2	D⁶D_1/2
42	Mo	molybdenum	6	[Kr] 4d⁵ 5s¹	⁷S₃	S⁷S₃
43	Tc	technetium	7	[Kr] 4d⁵ 5s²	⁶S_5/2	S⁶S_5/2
44	Ru	ruthenium	8	[Kr] 4d⁷ 5s¹	⁵F₅	F⁵F₅
45	Rh	rhodium	9	[Kr] 4d⁸ 5s¹	⁴F_9/2	F⁴F_9/2
46	Pd	palladium	10	[Kr] 4d¹⁰	¹S₀	S¹S₀
47	Ag	silver	11	[Kr] 4d¹⁰ 5s¹	²D_1/2	D²D_1/2
48	Cd	cadmium	12	[Kr] 4d¹⁰ 5s²	¹S₀	S¹S₀
49	In	indium	13	[Kr] 4d¹⁰ 5s² 5p¹	²P_¹⁄₂	P²P_¹⁄₂
50	Sn	tin	14	[Kr] 4d¹⁰ 5s² 5p²	³P₀	P³P₀
51	Sb	antimony	15	[Kr] 4d¹⁰ 5s² 5p³	⁴S_³⁄₂	S⁴S_³⁄₂
52	Te	tellurium	16	[Kr] 4d¹⁰ 5s² 5p⁴	³P₂	P³P₂
53	I	iodine	17	[Kr] 4d¹⁰ 5s² 5p⁵	²P_³⁄₂	P²P_³⁄₂
54	Xe	xenon	18	[Kr] 4d¹⁰ 5s² 5p⁶	¹S₀	S¹S₀
55	Cs	caesium	1	[Xe] 6s¹	²S_¹⁄₂	S²S_¹⁄₂
56	Ba	barium	2	[Xe] 6s²	¹S₀	S¹S₀
57	La	lanthanum	3	[Xe] 5d¹ 6s²	²D_3/2	D²D_3/2
58	Ce	cerium	n/a	[Xe] 4f¹ 5d¹ 6s²^[4]	¹G₄	G¹G₄
59	Pr	praseodymium	n/a	[Xe] 4f³ 6s²	⁴I_9/2	I⁴I_9/2
60	Nd	neodymium	n/a	[Xe] 4f⁴ 6s²	⁵I₄	I⁵I₄
61	Pm	promethium	n/a	[Xe] 4f⁵ 6s²	⁶H_5/2	H⁶H_5/2
62	Sm	samarium	n/a	[Xe] 4f⁶ 6s²	⁷F₀	F⁷F₀
63	Eu	europium	n/a	[Xe] 4f⁷ 6s²	⁸S_7/2	S⁸S_7/2
64	Gd	gadolinium	n/a	[Xe] 4f⁷ 5d¹ 6s²	⁹D₂	D⁹D₂
65	Tb	terbium	n/a	[Xe] 4f⁹ 6s²	⁶H_15/2	H⁶H_15/2
66	Dy	dysprosium	n/a	[Xe] 4f¹⁰ 6s²	⁵I₈	I⁵I₈
67	Ho	holmium	n/a	[Xe] 4f¹¹ 6s²	⁴I_15/2	I⁴I_15/2
68	Er	erbium	n/a	[Xe] 4f¹² 6s²	³H₆	H³H₆
69	Tm	thulium	n/a	[Xe] 4f¹³ 6s²	²F_7/2	F²F_7/2
70	Yb	ytterbium	n/a	[Xe] 4f¹⁴ 6s²	¹S₀	S¹S₀
71	Lu	lutetium	n/a	[Xe] 4f¹⁴ 5d¹ 6s²	²D_3/2	D²D_3/2
72	Hf	hafnium	4	[Xe] 4f¹⁴ 5d² 6s²	³F₂	F³F₂
73	Ta	tantalum	5	[Xe] 4f¹⁴ 5d³ 6s²	⁴F_3/2	F⁴F_3/2
74	W	tungsten	6	[Xe] 4f¹⁴ 5d⁴ 6s²^[5]	⁵D₀	D⁵D₀
75	Re	rhenium	7	[Xe] 4f¹⁴ 5d⁵ 6s²	⁶S_5/2	S⁶S_5/2
76	Os	osmium	8	[Xe] 4f¹⁴ 5d⁶ 6s²	⁵D₄	D⁵D₄
77	Ir	iridium	9	[Xe] 4f¹⁴ 5d⁷ 6s²	⁴F_9/2	F⁴F_9/2
78	Pt	platinum	10	[Xe] 4f¹⁴ 5d⁹ 6s¹	³D₃	D³D₃
79	Au	gold	11	[Xe] 4f¹⁴ 5d¹⁰ 6s¹	²D_1/2	D²D_1/2
80	Hg	mercury	12	[Xe] 4f¹⁴ 5d¹⁰ 6s²	¹S₀	S¹S₀
81	Tl	thallium	13	[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹	²P_¹⁄₂	P²P_¹⁄₂
82	Pb	lead	14	[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p²	³P₀	P³P₀
83	Bi	bismuth	15	[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p³	⁴S_³⁄₂	S⁴S_³⁄₂
84	Po	polonium	16	[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁴	³P₂	P³P₂
85	At	astatine	17	[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵	²P_³⁄₂	P²P_³⁄₂
86	Rn	radon	18	[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶	¹S₀	S¹S₀
87	Fr	francium	1	[Rn] 7s¹	²S_¹⁄₂	S²S_¹⁄₂
88	Ra	radium	2	[Rn] 7s²	¹S₀	S¹S₀
89	Ac	actinium	3	[Rn] 6d¹ 7s²	²D_3/2	D²D_3/2
90	Th	thorium	n/a	[Rn] 6d² 7s²	³F₂	F³F₂
91	Pa	protactinium	n/a	[Rn] 5f² 6d¹ 7s²	⁴K_11/2	K⁴K_11/2
92	U	uranium	n/a	[Rn] 5f³ 6d¹ 7s²	⁵L₆	L⁵L₆
93	Np	neptunium	n/a	[Rn] 5f⁴ 6d¹ 7s²	⁶L_11/2	L⁶L_11/2
94	Pu	plutonium	n/a	[Rn] 5f⁶ 7s²	⁷F₀	F⁷F₀
95	Am	americium	n/a	[Rn] 5f⁷ 7s²	⁸S_7/2	S⁸S_7/2
96	Cm	curium	n/a	[Rn] 5f⁷ 6d¹ 7s²	⁹D₂	D⁹D₂
97	Bk	berkelium	n/a	[Rn] 5f⁹ 7s²	⁶H_15/2	H⁶H_15/2
98	Cf	californium	n/a	[Rn] 5f¹⁰ 7s²^[6]	⁵I₈	I⁵I₈
99	Es	einsteinium	n/a	[Rn] 5f¹¹ 7s²	⁵I_15/2	I⁵I_15/2
100	Fm	fermium	n/a	[Rn] 5f¹² 7s²	³H₆	H³H₆
101	Md	mendelevium	n/a	[Rn] 5f¹³ 7s²	²F_7/2	F²F_7/2
102	No	nobelium	n/a	[Rn] 5f¹⁴ 7s²	¹S₀	S¹S₀
103	Lr	lawrencium	n/a	[Rn] 5f¹⁴ 7s² 7p¹	²P_1/2?	P²P_1/2?
104	Rf	rutherfordium	4	[Rn] 5f¹⁴ 6d² 7s²^[7]^[8]	³F₂	F³F₂
105	Db	dubnium	5	[Rn] 5f¹⁴ 6d³ 7s²^[8]	⁴F_3/2?	F⁴F_3/2?
106	Sg	seaborgium	6	[Rn] 5f¹⁴ 6d⁴ 7s²^[8]	⁵D₀?	D⁵D₀?
107	Bh	bohrium	7	[Rn] 5f¹⁴ 6d⁵ 7s²^[9]^[8]	⁶S_5/2?	S⁶S_5/2?
108	Hs	hassium	8	[Rn] 5f¹⁴ 6d⁶ 7s²^[8]
109	Mt	meitnerium	9	[Rn] 5f¹⁴ 6d⁷ 7s² (calculated)^[8]^[10]
110	Ds	darmstadtium	10	[Rn] 5f¹⁴ 6d⁸ 7s² (predicted)^[8]
111	Rg	roentgenium	11	[Rn] 5f¹⁴ 6d⁹ 7s² (predicted)^[11]^[8]
112	Cn	copernicium	12	[Rn] 5f¹⁴ 6d¹⁰ 7s² (predicted)^[8]
113	Nh	nihonium	13	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p¹ (predicted)^[8]
114	Fl	flerovium	14	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p² (predicted)^[8]
115	Mc	moscovium	15	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p³ (predicted)^[8]
116	Lv	livermorium	16	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁴ (predicted)^[8]
117	Ts	tennessine	17	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁵ (predicted)^[8]
118	Og	oganesson	18	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁶ (predicted)^[12]^[8]
119	Uue	ununennium	1	[Og] 8s¹ (predicted)^[8]
120	Ubn	unbinilium	2	[Og] 8s² (predicted)^[8]
121	Ubu	unbiunium	3	[Og] 8s² 8p¹ (predicted)^[8]

Term symbols for an electron configuration

The process to calculate all possible term symbols for a given electron configuration is somewhat longer.

First, the total number of possible microstates N is calculated for a given electron configuration. As before, the filled (sub)shells are discarded, and only the partially filled ones are kept. For a given orbital quantum number l, t is the maximum allowed number of electrons, t = 2(2l+1). If there are e electrons in a given subshell, the number of possible microstates is

N= {t \choose e} = {t! \over {e!\,(t-e)!}}.

As an example, consider the carbon electron structure: 1s²2s²2p². After removing full subshells, there are 2 electrons in a p-level (l = 1), so there are

N = {6! \over {2!\,4!}}=15

different microstates.

Second, all possible microstates are drawn. M_L and M_S for each microstate are calculated, with $M=\sum_{i=1}^e m_i$ where m_i is either m_l or m_s for the i-th electron, and M represents the resulting M_L or M_S respectively:

	+1	0	−1	M_L	M_S
	m_l
all up	↑	↑		1	1
	↑		↑	0	1
		↑	↑	−1	1
all down	↓	↓		1	−1
	↓		↓	0	−1
		↓	↓	−1	−1
one up one down	↑↓			2	0
	↑	↓		1	0
	↑		↓	0	0
	↓	↑		1	0
		↑↓		0	0
		↑	↓	−1	0
	↓		↑	0	0
		↓	↑	−1	0
			↑↓	−2	0

Third, the number of microstates for each M_L—M_S possible combination is counted:

		+1	0	−1
		M_S
M_L	+2		1
	+1	1	2	1
	0	1	3	1
	−1	1	2	1
	−2		1

Fourth, smaller tables can be extracted representing each possible term. Each table will have the size (2L+1) by (2S+1), and will contain only "1"s as entries. The first table extracted corresponds to M_L ranging from −2 to +2 (so L = 2), with a single value for M_S (implying S = 0). This corresponds to a ¹D term. The remaining terms fit inside the middle 3×3 portion of the table above. Then a second table can be extracted, removing the entries for M_L and M_S both ranging from −1 to +1 (and so S = L = 1, a ³P term). The remaining table is a 1×1 table, with L = S = 0, i.e., a ¹S term.

S = 0, L = 2, J = 2
¹D₂
		0
		M_s
M_l	+2	1
	+1	1
	0	1
	−1	1
	−2	1

S=1, L=1, J=2,1,0
³P₂, ³P₁, ³P₀
		+1	0	−1
		M_s
M_l	+1	1	1	1
	0	1	1	1
	−1	1	1	1

S=0, L=0, J=0
¹S₀
		0
		M_s
M_l	0	1

Fifth, applying Hund's rules, the ground state can be identified (or the lowest state for the configuration of interest.) Hund's rules should not be used to predict the order of states other than the lowest for a given configuration. (See examples at Hund's rules#Excited states.)
If only two equivalent electrons are involved, there is an "Even Rule" which states that, for two equivalent electrons, the only states that are allowed are those for which the sum (L + S) is even.

Case of three equivalent electrons

For three equivalent electrons (with the same orbital quantum number l), there is also a general formula (denoted by X(L,S,l) below) to count the number of any allowed terms with total orbital quantum number "L" and total spin quantum number "S".

$X(L,S,l)= \begin{cases} L-\lfloor\frac{L}{3}\rfloor, & \text{if }S=1/2\text{ and } 0\leq L <l\\ l-\lfloor\frac{L}{3}\rfloor, & \text{if }S=1/2\text{ and } l\leq L \leq 3l-1 \\ \lfloor \frac{L}{3}\rfloor -\lfloor \frac{L-l}{2} \rfloor +\lfloor \frac{L-l+1}{2} \rfloor, & \text{if }S=3/2\text{ and } 0\leq L <l \\ \lfloor \frac{L}{3} \rfloor -\lfloor \frac{L-l}{2} \rfloor, & \text{if }S=3/2\text{ and } l\leq L \leq 3l-3 \\ 0, & \text{ other cases} \end{cases}$

where the floor function $\lfloor x \rfloor$ denotes the greatest integer not exceeding x.

The detailed proof can be found in Renjun Xu's original paper.^[13]

For a general electronic configuration of l^k, namely k equivalent electrons occupying one subshell, the general treatment and computer code can also be found in this paper.^[13]

Alternative method using group theory

For configurations with at most two electrons (or holes) per subshell, an alternative and much quicker method of arriving at the same result can be obtained from group theory. The configuration 2p² has the symmetry of the following direct product in the full rotation group:

Γ⁽¹⁾ × Γ⁽¹⁾ = Γ⁽⁰⁾ + [Γ⁽¹⁾] + Γ⁽²⁾,

which, using the familiar labels Γ⁽⁰⁾ = S, Γ⁽¹⁾ = P and Γ⁽²⁾ = D, can be written as

P × P = S + [P] + D.

The square brackets enclose the anti-symmetric square. Hence the 2p² configuration has components with the following symmetries:

S + D (from the symmetric square and hence having symmetric spatial wavefunctions);

P (from the anti-symmetric square and hence having an anti-symmetric spatial wavefunction).

The Pauli principle and the requirement for electrons to be described by anti-symmetric wavefunctions imply that only the following combinations of spatial and spin symmetry are allowed:

¹S + ¹D (spatially symmetric, spin anti-symmetric)

³P (spatially anti-symmetric, spin symmetric).

Then one can move to step five in the procedure above, applying Hund's rules.

The group theory method can be carried out for other such configurations, like 3d², using the general formula

Γ^(j) × Γ^(j) = Γ^(2j) + Γ^(2j-2) + ... + Γ⁽⁰⁾ + [Γ^(2j-1) + ... + Γ⁽¹⁾].

The symmetric square will give rise to singlets (such as ¹S, ¹D, & ¹G), while the anti-symmetric square gives rise to triplets (such as ³P & ³F).

More generally, one can use

Γ^(j) × Γ^(k) = Γ^(j+k) + Γ^(j+k−1) + ... + Γ^(|j−k|)

where, since the product is not a square, it is not split into symmetric and anti-symmetric parts. Where two electrons come from inequivalent orbitals, both a singlet and a triplet are allowed in each case. ^[14]

Summary of various coupling schemes and corresponding term symbols

Basic concepts for all coupling schemes:

${\overrightarrow {l}}$ : individual orbital angular momentum vector for an electron, ${\overrightarrow {s}}$ : individual spin vector for an electron, ${\overrightarrow {j}}$ : individual total angular momentum vector for an electron, ${\overrightarrow {j}}={\overrightarrow {l}}+{\overrightarrow {s}}$ .
${\overrightarrow {L}}$ : Total orbital angular momentum vector for all electrons in an atom ( ${\overrightarrow {L}}=\sum _{i}{\overrightarrow {l_{i}}}$ ).
${\overrightarrow {S}}$ : total spin vector for all electrons ( ${\overrightarrow {S}}=\sum _{i}{\overrightarrow {s_{i}}}$ ).
${\overrightarrow {J}}$ : total angular momentum vector for all electrons. The way the angular momenta are combined to form ${\overrightarrow {J}}$ depends on the coupling scheme: ${\overrightarrow {J}}={\overrightarrow {L}}+{\overrightarrow {S}}$ for LS coupling, ${\overrightarrow {J}}=\sum _{i}{\overrightarrow {j_{i}}}$ for jj coupling, etc.
A quantum number corresponding to the magnitude of a vector is a letter without an arrow (ex: l is the orbital angular momentum quantum number for ${\overrightarrow {l}}$ and ${{\hat {l}}^{2}}\left|l,m,\ldots \right\rangle ={{\hbar }^{2}}l\left(l+1\right)\left|l,m,\ldots \right\rangle$ )
The parameter called multiplicity represents the number of possible values of the total angular momentum quantum number J for certain conditions.
For a single electron, the term symbol is not written as S is always 1/2 and L is obvious from the orbital type.
For two electron groups A and B with their own terms, each term may represent S, L and J which are quantum numbers corresponding to the ${\overrightarrow {S}}$ , ${\overrightarrow {L}}$ and ${\overrightarrow {J}}$ vectors for each group. "Coupling" of terms A and B to form a new term C means finding quantum numbers for new vectors ${\overrightarrow {S}}={\overrightarrow {S_{A}}}+{\overrightarrow {S_{B}}}$ , ${\overrightarrow {L}}={\overrightarrow {L_{A}}}+{\overrightarrow {L_{B}}}$ and ${\overrightarrow {J}}={\overrightarrow {L}}+{\overrightarrow {S}}$ . This example is for LS coupling and which vectors are summed in a coupling is depending on which scheme of coupling is taken. Of course, the angular momentum addition rule is that $X=X_{A}+X_{B},X_{A}+X_{B}-1,...,|X_{A}-X_{B}|$ where X can be s, l, j, S, L, J or any other angular momentum-magnitude-related quantum number.

LS coupling (Russell-Saunders coupling)

Coupling scheme: ${\overrightarrow {L}}$ and ${\overrightarrow {S}}$ are calculated first then ${\overrightarrow {J}}={\overrightarrow {L}}+{\overrightarrow {S}}$ is obtained. In practical point of view, it means L, S and J are obtained by using addition rule of angular momentums with given electronics groups that are to be coupled.
Electronic configuration + Term symbol: $n{{l}^{N}}{{(}^{(2S+1)}}{{L}_{J}})$ . ${{(}^{(2S+1)}}{{L}_{J}})$ is a Term which is from coupling of electrons in $n{{l}^{N}}$ group. n,l are principle quantum number, orbital quantum number and $n{{l}^{N}}$ means there are N (equivalent) electrons in nl subshell. For $L>S$ , (2S+1) is equal to multiplicity, a number of possible values in J (final total angular momentum quantum number) from given S and L. For $S>L$ , multiplicity is (2L+1) but (2S+1) is still written in the Term symbol. Strictly speaking, ${{(}^{(2S+1)}}{{L}_{J}})$ is called Level and ${^{\left(2S+1\right)}{L}}$ is called Term. Sometimes superscript o is attached to the Term, means the parity $P={{\left(-1\right)}^{{\underset {i}{\mathop {\sum } }}\,{{l}_{i}}}}$ of group is odd (P = -1).
Example:
1. $3{{d}^{7}}{{{\text{ }}\!\!~\!\!{\text{ }}}\ ^{4}}{{F}_{7/2}}$ : $^{4}{{F}_{7/2}}$ is Level of 3d⁷ group in which are equivalent 7 electrons are in 3d subshell.
2. $3{{d}^{7}}{{(}^{4}}F)4s4p{{(}^{3}}{{p}^{0}}){{\text{ }}\ ^{6}}F_{9/2}^{0}$ : Terms are assigned for each group (with different principal quantum number n) and rightmost Level ${^{6}{{\text{F}}_{9/2}^{o}}}$ is from coupling of Terms of these groups so ${^{6}{{\text{F}}_{9/2}^{o}}}$ represents final total spin quantum number S, total orbital angular momentum quantum number L and total angular momentum quantum number J in this atomic energy level.
3. $4{{f}^{7}}\left(^{8}{{S}^{0}}\right)5d\ \ \left(^{7}{{D}^{o}}\right)6p\ \ ^{8}F_{13/2}^{0}$ : There is a space between 5d and $\left(^{7}{{D}^{o}}\right)$ . It means $\left(^{8}{{S}^{0}}\right)$ and 5d are coupled to get $\left(^{7}{{D}^{o}}\right)$ . Final level ${^{8}{F_{13/2}^{o}}}$ is from coupling of $\left(^{7}{{D}^{o}}\right)$ and 6p.
4. $4f\left(^{2}{{F}^{0}}\right)\ \ 5{{d}^{2}}\left(^{1}G\right)6s\ \ {{\left(^{2}G\right)}\ \ ^{1}}P_{1}^{0}$ : There is only one Term $\left({^{2}{{F}^{o}}}\right)$ which is isolated in the left of the leftmost space. It means $\left({^{2}{{F}^{o}}}\right)$ is coupled lastly; $\left({^{1}{G}}\right)$ and 6s are coupled to get $\left({^{2}{G}}\right)$ then $\left({^{2}{G}}\right)$ and $\left({^{2}{{F}^{o}}}\right)$ are coupled to get final Term ${^{1}{P_{1}^{o}}}$ .

jj Coupling

Coupling scheme: ${\overrightarrow {J}}=\sum _{i}{\overrightarrow {j_{i}}}$ .
Electronic configuration + Term symbol: ${{\left({{n}_{1}}{{l}_{1}}_{{j}_{1}}^{{N}_{1}}{{n}_{2}}{{l}_{2}}_{{j}_{2}}^{{N}_{2}}\ldots \right)}_{J}}$
Example:
1. ${{\left(6p_{\frac {1}{2}}^{2}6p_{\frac {3}{2}}^{}\right)}^{o}}_{3/2}$ : There are two groups. One is $6p_{1/2}^{2}$ and the other is $6p_{\frac {3}{2}}^{}$ . In $6p_{1/2}^{2}$ , there are 2 electrons having $j=1/2$ in 6p subshell while there is an electron having $j=3/2$ in the same subshell in $6p_{\frac {3}{2}}^{}$ .Coupling of these two groups results in J = 3/2 (coupling of j of three electrons).
2. $4d_{5/2}^{3}4d_{3/2}^{2}~\ {{\left({\frac {9}{2}},2\right)}_{11/2}}$ : 9/2 in () is ${{J}_{1}}$ for 1st group $4d_{5/2}^{3}$ and 2 in () is J₂ for 2nd group $4d_{3/2}^{2}$ . Subscript 11/2 of Term symbol is final J of ${\overrightarrow {J}}={\overrightarrow {J_{1}}}+{\overrightarrow {J_{2}}}$ .

J₁L₂ coupling

Coupling scheme: ${\overrightarrow {K}}={\overrightarrow {J_{1}}}+{\overrightarrow {L_{2}}}$ and ${\overrightarrow {J}}={\overrightarrow {K}}+{\overrightarrow {S_{2}}}$ .
Electronic configuration + Term symbol: ${{n}_{1}}{{l}_{1}}^{{N}_{1}}\left(Ter{{m}_{1}}\right){{n}_{2}}{{l}_{2}}^{{N}_{2}}\left(Ter{{m}_{2}}\right)~\ {^{\left(2{{S}_{2}}+1\right)}{{\left[K\right]}_{J}}}$ . For K > S₂, (2S₂+1) is equal to multiplicity, a number of possible values in J (final total angular momentum quantum number) from given S₂ and K. For S₂ > K, multiplicity is (2K + 1) but (2S₂ + 1) is still written in the Term symbol.
Example:
1. $3{{p}^{5}}\left({^{2}{P_{\frac {1}{2}}^{o}}}\right)5g~\ {^{2}{\left[9/2\right]_{5}^{o}}}$ : ${{J}_{1}}={\frac {1}{2}},{{l}_{2}}=4,~{{s}_{2}}=1/2$ . 9/2 is K, which comes from coupling of J₁ and l₂. Subscript 5 in Term symbol is J which is from coupling of K and s₂.
2. $4{{f}^{13}}\left({^{2}{F_{\frac {7}{2}}^{o}}}\right)5{{d}^{2}}\left({^{1}{D}}\right)\ ~{^{1}{\left[7/2\right]_{7/2}^{o}}}$ : ${{J}_{1}}={\frac {7}{2}},{{L}_{2}}=2,~{{S}_{2}}=0$ . 7/2 is K, which comes from coupling of J₁ and L₂. Subscript 7/2 in Term symbol is J which is from coupling of K and S₂.

LS₁ coupling

Coupling scheme: ${\overrightarrow {K}}={\overrightarrow {L}}+{\overrightarrow {S_{1}}}$ , ${\overrightarrow {J}}={\overrightarrow {K}}+{\overrightarrow {S_{2}}}$ .
Electronic configuration + Term symbol: ${{n}_{1}}{{l}_{1}}^{{N}_{1}}\left(Ter{{m}_{1}}\right){{n}_{2}}{{l}_{2}}^{{N}_{2}}\left(Ter{{m}_{2}}\right)\ ~L~\ {^{\left(2{{S}_{2}}+1\right)}{{\left[K\right]}_{J}}}$ . For K > S₂, (2S₂ + 1) is equal to multiplicity, a number of possible values in J (final total angular momentum quantum number) from given S₂ and K. For S₂ > K, multiplicity is (2K+1) but (2S₂ + 1) is still written in the Term symbol.
Example:
1. $3{{\text{d}}^{7}}\left({^{4}{P}}\right)4s4p\left({^{3}{{P}^{o}}}\right)\ ~{{D}^{o}}~\ {^{3}{\left[5/2\right]_{7/2}^{o}}}$ : ${{L}_{1}}=1,~{{L}_{2}}=1,~{{S}_{1}}={\frac {3}{2}},~{{S}_{2}}=1$ . $L=2,K=5/2,J=7/2$ .

Most famous coupling schemes are introduced here but these schemes can be mixed together to express energy state of atom. This summary is based on .

Racah notation and Paschen notation

These are notations for describing states of singly excited atoms, especially noble gas atoms. Racah notation is basically a combination of LS or Russell-Saunder coupling and J₁L₂ coupling. LS coupling is for a parent ion and J₁L₂ coupling is for an coupling of the parent ion and the excited electron. The parent ion is an unexcited part of the atom. For example, in Ar atom excited from a ground state …3p⁶ to an excited state …3p⁵4p in electronic configuration, 3p⁵ is for the parent ion while 4p is for the excited electron.^[15]

In Racah notation, states of excited atoms are denoted as $\left(^{\left(2{{S}_{1}}+1\right)}{{L}_{1}}_{{J}_{1}}\right)nl\left[K\right]_{J}^{o}$ . Quantities with a subscript 1 are for the parent ion, n and l are principal and orbital quantum numbers for the excited electron, K and J are quantum numbers for ${\overrightarrow {K}}={\overrightarrow {{J}_{1}}}+{\vec {l}}$ and ${\overrightarrow {J}}={\overrightarrow {K}}+{\vec {s}}$ where ${\vec {l}}$ and ${\vec {s}}$ are orbital angular momentum and spin for the excited electron respectively. “o” represents a parity of excited atom. For an inert (noble) gas atom, usual excited states are Np⁵nl where N = 2, 3, 4, 5, 6 for Ne, Ar, Kr, Xe, Rn, respectively in order. Since the parent ion can only be ²P_1/2 or ²P_3/2, the notation can be shortened to $nl\left[K\right]_{J}^{o}$ or $nl'\left[K\right]_{J}^{o}$ , where nl means the parent ion is in ²P_3/2 while nl′ is for the parent ion in ²P_1/2 state.

Paschen notation is a somewhat odd notation; it is an old notation made to attempt to fit an emission spectrum of neon to a hydrogen-like theory. It has a rather simple structure to indicate energy levels of an excited atom. The energy levels are denoted as n’l#. l is just an orbital quantum number of the excited electron. n'l is written in a way that 1s for (n = N + 1, l = 0), 2p for (n = N + 1, l = 1), 2s for (n = N + 2, l = 0), 3p for (n = N + 2, l = 1), 3s for (n = N + 3, l = 0), etc. Rules of writing n'l from the lowest electronic configuration of the excited electron are: (1) l is written first, (2) n' is consecutively written from 1 and the relation of l = n' - 1, n' - 2, ... , 0 (like a relation between n and l) is kept. n'l is an attempt to describe electronic configuration of the excited electron in a way of describing electronic configuration of hydrogen atom. # is an additional number denoted to each energy level of given n'l (there can be multiple energy levels of given electronic configuration, denoted by the term symbol). # denotes each level in order, for example, # = 10 is for a lower energy level than # = 9 level and # = 1 is for the highest level in a given n’l. An example of Paschen notation is below.

Electronic configuration of Neon	n’l	Electronic configuration of Argon	n’l
1s²2s²2p⁶	Ground state	[Ne]3s²3p⁶	Ground state
1s²2s²2p⁵3s¹	1s	[Ne]3s²3p⁵4s¹	1s
1s²2s²2p⁵3p¹	2p	[Ne]3s²3p⁵4p¹	2p
1s²2s²2p⁵4s¹	2s	[Ne]3s²3p⁵5s¹	2s
1s²2s²2p⁵4p¹	3p	[Ne]3s²3p⁵5p¹	3p
1s²2s²2p⁵5s¹	3s	[Ne]3s²3p⁵6s¹	3s

Notes

↑ There is no official convention for naming angular momentum values greater than 20 (symbol Z). Many authors begin using Greek letters at this point ( $\alpha,\beta, \gamma,$ ...). The occasions for which such notation is necessary are few and far between, however.

References

1 2 NIST Atomic Spectrum Database To read neutral carbon atom levels for example, type "C I" in the Spectrum box and click on Retrieve data.
↑ Levine, Ira N., Quantum Chemistry (4th ed., Prentice-Hall 1991), ISBN 0-205-12770-3
↑ Jaccaud et al. 2000, p. 381.
↑ Ground levels and ionization energies for the neutral atoms, NIST
↑ Berger, Dan. "Why does Tungsten not 'Kick' up an electron from the s sublevel ?". Bluffton College, USA.
↑ CRC 2006, p. 1.14.
↑
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Hoffman, Darleane C.; Lee, Diana M.; Pershina, Valeria (2006). "Transactinides and the future elements". In Morss; Edelstein, Norman M.; Fuger, Jean. The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer Science+Business Media. ISBN 1-4020-3555-1.
↑ Johnson, E.; Fricke, B.; Jacob, T.; Dong, C. Z.; Fritzsche, S.; Pershina, V. (2002). "Ionization potentials and radii of neutral and ionized species of elements 107 (bohrium) and 108 (hassium) from extended multiconfiguration Dirac–Fock calculations". The Journal of Chemical Physics. 116: 1862. Bibcode:2002JChPh.116.1862J. doi:10.1063/1.1430256.
↑ Thierfelder, C.; Schwerdtfeger, P.; Heßberger, F. P.; Hofmann, S. (2008). "Dirac-Hartree-Fock studies of X-ray transitions in meitnerium". The European Physical Journal A. 36 (2): 227. Bibcode:2008EPJA...36..227T. doi:10.1140/epja/i2008-10584-7.
↑ Turler, A. (2004). "Gas Phase Chemistry of Superheavy Elements" (PDF). Journal of Nuclear and Radiochemical Sciences. 5 (2): R19–R25.
↑ Nash, Clinton S. (2005). "Atomic and Molecular Properties of Elements 112, 114, and 118". Journal of Physical Chemistry A. 109 (15): 3493–3500. Bibcode:2005JPCA..109.3493N. doi:10.1021/jp050736o. PMID 16833687.
1 2 Xu, Renjun; Zhenwen, Dai (2006). "Alternative mathematical technique to determine LS spectral terms". Journal of Physics B: Atomic, Molecular and Optical Physics. 39 (16): 3221–3239. arXiv:physics/0510267. Bibcode:2006JPhB...39.3221X. doi:10.1088/0953-4075/39/16/007.
↑ McDaniel, Darl H. (1977). "Spin factoring as an aid in the determination of spectroscopic terms". Journal of Chemical Education. 54 (3): 147. Bibcode:1977JChEd..54..147M. doi:10.1021/ed054p147.
↑ "APPENDIX 1 - Coupling Schemes and Notation" (PDF). University of Toronto: Advanced Physics Laboratory - Course Homepage. Retrieved 5 Nov 2017.

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[3] There is no official convention for naming angular momentum values greater than 20 (symbol Z). Many authors begin using Greek letters at this point ( $\alpha,\beta, \gamma,$ ...). The occasions for which such notation is necessary are few and far between, however.

[NIST-1] 1 2 NIST Atomic Spectrum Database To read neutral carbon atom levels for example, type "C I" in the Spectrum box and click on Retrieve data.

[2] Levine, Ira N., Quantum Chemistry (4th ed., Prentice-Hall 1991), ISBN 0-205-12770-3

[FOOTNOTEJaccaud_et_al.2000381-4] Jaccaud et al. 2000, p. 381.

[5] Ground levels and ionization energies for the neutral atoms, NIST

[6] Berger, Dan. "Why does Tungsten not 'Kick' up an electron from the s sublevel ?". Bluffton College, USA.

[FOOTNOTECRC20061.14-7] CRC 2006, p. 1.14.

[rsc-8] ↑

[Haire-9] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Hoffman, Darleane C.; Lee, Diana M.; Pershina, Valeria (2006). "Transactinides and the future elements". In Morss; Edelstein, Norman M.; Fuger, Jean. The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer Science+Business Media. ISBN 1-4020-3555-1.

[ioniz-10] Johnson, E.; Fricke, B.; Jacob, T.; Dong, C. Z.; Fritzsche, S.; Pershina, V. (2002). "Ionization potentials and radii of neutral and ionized species of elements 107 (bohrium) and 108 (hassium) from extended multiconfiguration Dirac–Fock calculations". The Journal of Chemical Physics. 116: 1862. Bibcode:2002JChPh.116.1862J. doi:10.1063/1.1430256.

[11] Thierfelder, C.; Schwerdtfeger, P.; Heßberger, F. P.; Hofmann, S. (2008). "Dirac-Hartree-Fock studies of X-ray transitions in meitnerium". The European Physical Journal A. 36 (2): 227. Bibcode:2008EPJA...36..227T. doi:10.1140/epja/i2008-10584-7.

[e-conf-12] Turler, A. (2004). "Gas Phase Chemistry of Superheavy Elements" (PDF). Journal of Nuclear and Radiochemical Sciences. 5 (2): R19–R25.

[Nash2005-13] Nash, Clinton S. (2005). "Atomic and Molecular Properties of Elements 112, 114, and 118". Journal of Physical Chemistry A. 109 (15): 3493–3500. Bibcode:2005JPCA..109.3493N. doi:10.1021/jp050736o. PMID 16833687.

[Xu-14] 1 2 Xu, Renjun; Zhenwen, Dai (2006). "Alternative mathematical technique to determine LS spectral terms". Journal of Physics B: Atomic, Molecular and Optical Physics. 39 (16): 3221–3239. arXiv:physics/0510267. Bibcode:2006JPhB...39.3221X. doi:10.1088/0953-4075/39/16/007.

[15] McDaniel, Darl H. (1977). "Spin factoring as an aid in the determination of spectroscopic terms". Journal of Chemical Education. 54 (3): 147. Bibcode:1977JChEd..54..147M. doi:10.1021/ed054p147.

[16] "APPENDIX 1 - Coupling Schemes and Notation" (PDF). University of Toronto: Advanced Physics Laboratory - Course Homepage. Retrieved 5 Nov 2017.