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What is the ground state molecular term symbol for $\ce{HF}$?

My attempt went like this: I drew the molecular orbital diagram and found that in the ground state, the highest energy MOs were two degenerate orbitals with 2 electrons each. Since there are no unpaired electrons, the term symbol assigned should convey the the information: (1) $\Lambda = 0$, (2) Spin multiplicity of 1, and (3) symmetric or anti-symmetric about a defined mirror plane containing the internuclear axis.

With information (1) and (2), the term symbol I obtained is $^1\Sigma$. But, I am not entirely sure about information (3), should it be $^1\Sigma^+$ or $^1\Sigma^-$?

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    $\begingroup$ The +, - symbol refer to the symmetry of the electronic wavefunction with respect to the molecular plane of symmetry. In this case is symmetric so you shoud use a +. $\endgroup$
    – PAEP
    Commented Nov 5 at 6:25
  • $\begingroup$ A good general reference on the topic Daniel Harris & Michael Bertolucci, Symmetry and Spectroscopy: an introduction to vibrational and electronic spectroscopy, New York, Dover Publications (1989). $\endgroup$
    – PAEP
    Commented Nov 5 at 6:28

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