Spectroscopic term symbols

Each separate energy level is given a label called a (spectroscopic) term symbol. For the moment it is sufficient to regard these merely as labels. See Further Reading at the end of this chapter for mote information. 

The spectroscopic term symbols for the molecular case can be obtained,... 

As the electronic energy of an atom or ion will depend on the quantum numbers , S, and J, we designate the various energy states which may arise from a given electronic configuration by what is known as a spectroscopic term symbol ... 

The spectroscopic term symbol for the electronic configuration 2P13p] 3d1 system, calculated ... 

In a manner similar to that by which the atomic states were designated as s, p, d, or /, the letters S, P, D, and F correspond to the values of 0, 1, 2, and 3, respectively, for the angular momentum vector, L. After the values of the vectors L, S, and / have been determined, the overall angular momentum is described by a symbol known as a term symbol or spectroscopic state. This symbol is constructed as Ps+1)Lj where the appropriate letter is used for the L value as listed earlier, and the quantity (2S + 1) is known as the multiplicity. For one unpaired electron, (2S + 1) = 2, and a multiplicity of 2 gives rise to a doublet. For two unpaired electrons, the multiplicity is 3, and the state is called a triplet state. 

In an atomic term symbol the value of L = 1,2,..., etc. is coded according to spectroscopic notation as 5, P, D,F,G,... etc. (alphabetically for L > 3). Likewise, each atomic state can be characterized by a total electronic spin quantum number S,... 

A.12-1 for a brief review of atomic-spectroscopic notation). In a given term-symbol, T will be S, P, D, F, or G etc. depending on whether the total electronic orbital angular-momentum quantum number L is 0, 1,... 

A. 12-1. Spectroscopic states end term symbols for meny-electron atoms or ions... 

The electronic configuration and the RusseiKSaunders term symbols for the elements as determined spectroscopically or as predicted are given in Table 2-4. It must be emphasized that these electronic con-... 

It is recommended (REC. 38) that the wave number or frequency of any spectroscopic transition be expressed (corresponding to RECS. 29-31 for term symbols and formulas) in the general form... 

We are now in position to derive the electronic states arising from a given electronic configuration. These states have many names spectroscopic terms (or states), term symbols, and Russell-Saunders terms, in honor of spectroscopists H. N. Russell and F. A. Saunders. Hence, the scheme we use to derive these states is called Russell-Saunders coupling. It is also simply referred to as L-S coupling. 

Figure 3.10 Partial energy level diagram for the Fe3+ or Mn2+ ions with 3tfi configurations in high-spin states in an octahedral crystal field. Only sextet and quartet spectroscopic terms and crystal field states are shown. Note that the same energy level diagram applies to the cations in tetrahedral crystal fields (with g subscripts omitted from the state symbols for the acentric coordination site).

Atomic number Symbol Configuration (spectroscopic term) ... 

A.12-1. Spectroscopic states and term symbols for many-electron atoms or... 

This is called a term symbol. It represents a set of energy levels, called a term in spectroscopic parlance. States with a multiplicity of 1 are called singlet states, states with a multiplicity of 2 are called doublet states, states with a multiplicity of three are called triplets, states with a multiplicity of 4 are called quartets and so on. Hence, S is called singlet S, and is called triplet P. 

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