On the reflection symmetries of atoms and diatomic molecules: derivation of Σ+ and Σ− states in terms of the united atom and electron configurationKoichiro Yamakawa and Katsuyuki FukutaniEur. Phys. J. D, 69 7 (2015) 175DOI: https://doi.org/10.1140/epjd/e2015-60142-4