Static Jahn-Teller distortions in the small molecules: CH+4, CF+<>4, NH+3 (excited state) and NH3 (excited state)

The potential-energy curves corresponding to arbitrary displacements of the atoms in the four small molecules concerned have been estimated by the use of the Hellmami-Feynman theorem, and some simple assumptions about the location and distribution of the total electronic charge. Some necessary values of the relevant force constants are taken from spectroscopic work. It is shown that in CH+4 and the excited state of NH+3, where the electron has been taken from a bonding orbital, the static Jahn-Teller displacement in the equilibrium configuration is large, and in CH+4 the important normal co-ordinate increases by as much as 0.23 Å. In CF+4 and the excited state of NH3, where the bonding electrons are almost unaffected, the static distortion is much less, and is of the order of 0.02 Å for the important co-ordinate in CF+4.