Term symbol

Term symbols are used in quantum chemistry and quantum physics for atomic nuclei , atoms and molecules to denote energy levels .

The word term has been used to denote an energy level since Bohr's atomic model was used to recognize that the two mathematical terms in the Rydberg formula (the difference between which indicates the energy of the emitted light quanta ) correspond to the energies of two stationary states .

Atomic physics

A term symbol in atomic physics is composed of the quantum numbers for: ${\displaystyle {}^{2S+1}L_{J}}$

• the total electronic orbital angular momentum ; instead of the numerical values ​​of , the following letters are used (without the J to avoid confusion with the total angular momentum): ${\displaystyle L}$ ${\displaystyle L}$

el. orbital angular momentum ${\displaystyle L}$	0	1	2	3	4th	5	6th	7th	...
Code letter	S.	P	D.	F.	G	H	I.	K	...

• the multiplicity of the total spin ${\displaystyle 2S+1}$ ${\displaystyle S}$
• the total angular momentum ; This can have the following values: . ${\displaystyle J}$ ${\displaystyle J=|L-S|,|L-S|+1,...,L+S-1,L+S}$

For example, the term symbol of the ground state of the electron in the hydrogen atom is ² S _1/2 . It says:

• the central symbol S for an electronic orbital angular momentum  L = 0
• the left superscript 2 for the multiplicity 2 S +1, so here spin  S = ½
• the right subscript ½ of the total angular momentum  J .

Nuclear physics

A term symbol of nuclear physics called ${\displaystyle I^{\pm }}$

• the total angular momentum of the atomic nucleus ${\displaystyle I}$
• by the superscript sign the parity (i.e. the symmetry property of the wave function when reflected).

See also

• Term scheme
• Hund's rules