Saturday, June 9, 2018

quantum mechanics - Using ML and MS to determine existence of terms


When it comes to deciding which terms exist for a given configuration I have often seen an argument along the following lines:



For the configuration np2 with S=1 it is impossible to form a state with ML=2 without violation of the Pauli-exclusion principle. This then implies that the term 3D does not exist for the state configuration np2.




I have am looking for an explanation why the latter sentence must follow the former. Since it is possible to have a wave function with L=2 but ML=1 (say) which this statement does not seem to forbid. It is apparently (see e.g. Foot 2005, p 95) likewise possible to deduce that the terms 1P and 3S do not exist via a similar method. I am confused about how we can deduce the existence of a term simply by looking at the allowed values of MS and ML. Please can someone explain?




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