Term symbols

The term symbol for the total electronic configuration depends on the occupied electronic states. Full states have A-Symmetry, i.e. they are totally symmetric and need no further consideration. Partially occupied states are subject to multiplication as described in the chapter product rules.

Ci
Ag Au
Ag Ag Au
Au Au Ag
Cs
A' A''
A' A' A''
A'' A'' A'
C2
A B
A A B
B B A
C2h
A1 A2
A1 A1 A2
A2 A2 A1
   
     
C2v
A1 A2 B1 B2
A1 A1 A2 B1 B2
A2 A2 A1 B2 B1
B1 B1 B2 A1 A2
B2 B2 B1 A2 A1

Examples for the determination of the total electronic configuration

Cs:    One electron occupies an a', a second an a" state:

(a')1 (a'')1 yields configuration a' x a''  =  a''  ≡  A''

If the spin is antiparallel, the result is the singlett state 1A'', otherwise triplett state 3A''.

C2v:   Two electrons are in state b2 (e.g. H2O)

(b2)2  →   b2 x b2  =  a1  ≡   A1  →   1A1

Alternatively, if one electron is in state b2 and the other in a1 as in an excited state of the water molecule, two possible total electronic configurations result.

(b2)1 (a1)1  →  b2 x a1  =  b2  =  B2    → 1B2 or 3B2


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