I get the microstate-counting approach to finding the term symbols for a given configuration. But based on what I know about addition of angular momentum in quantum mechanics, I feel like there's a conceptual gap. When I do the microstate counting on the 2p##^{2}## configuration, I get singlet S, triplet P, and singlet D states. But when I add two electrons with l = 1 and s = 1/2, I get singlet S, singlet P, triplet P, and singlet D.(adsbygoogle = window.adsbygoogle || []).push({});

To clarify what I mean by adding these two electrons, I mean that I add the two orbital angular momenta l =1 to get values of L = 0,1,2, and I add the two spin angular momenta s = 1/2 to get values of S = 0,1. I then look at all six of these hypothetical states and eliminate the ones that violate the Pauli principle, namely the triplet D and triplet S. (These would violate the Pauli principle because they would require electrons with parallel spin AND parallel orbital angular momenta.) However, this leaves me with the extra singlet P state that does not appear in the microstate counting treatment. Where is my misconception here? What is forbidden about the singlet P state?

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# I LS-Coupling: intuition why 2p^2 has no singlet P?

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