NF - mysteries of a small molecule
Nitrogen fluoride (NF) seems like a very simple molecule and you would think it would very well understood, particularly as it is small enough that it is accessible to high level quantum chemistry calculations. However, the molecule exhibits some subtle properties that present a theoretical challenge. There is limited experimental data because the molecule is only found as an intermediate in some chemical reactions. Just like oxygen (O2), to which it is isoelectronic, the ground state is a triplet due to Hund's rule, as discussed for O2 here. I just read a nice paper A Valence Bond Study of the Low-Lying States of the NF Molecule Peifeng Su, Wei Wu, Sason Shaik, and Philippe C. Hiberty Given that F is more electronegative than N one might expect the ground state to have a large electric dipole moment and this to increase as the molecule is stretched. However, the ground state has only a small moment, it has the opposite direction to that expected from the electronegativ