Hunds rules on spectroscopic terms

When there are many terms arising from a given configuration, it would be of interest to know the relative order of their energies, or at least which is the ground term. To accomplish this, we make use of Hund s rule, in honor of physicist F. Hund  

Before leaving this topic, we once again note that electronic transitions occur between states and may or may not involve a change in configuration. Take the states in Fig. 2.3.2 as an example. Transition from ground state 3Po to excited state lD2 (3Pq lDi) [note that this is not an allowed transition in the first 

Energies of the spectroscopic state for the ground state configuration of carbon (not to scale ). 

To conclude this section, we illustrate how to obtain the ground term of a given configuration without writing out all the microstates. Again we take p2 as an example. When we place there two electrons into the three p orbitals we bear in mind that the ground term requires the maximum S (first priority) and L values. To achieve this, we place the electron in the following manner  

Since Ml runs from L to -L and Ms runs from S to -S, the maximum L and maximum S values are both 1 in this case. Hence, the ground term is 3P. 

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