The Jahn-Teller effect in NH₃⁺

The vertical ionization potential corresponding to the ²E ionic state of ammonia has been calculated on the Hartree-Fock level and by a Green’s function method taking account of many-body effects. Additional calculations have been performed on the same level of approximation to obtain the linear coupling constants between the electronic and nuclear motions. The Jahn-Teller hamiltonian has been diagonalized numerically and the full spectrum corresponding to the photoionization of an e-electron has been computed. The position and shape of the corresponding band in the experimental photoelectron spectrum are satisfactorily reproduced. Furthermore, an approximate solution of the Jahn-Teller hamiltonian is presented. The results compare well with those obtained by numerical diagonalization.