Potential energy function and rotation-vibration energy levels of NH 3+

Abstract

The potential energy surface for the electronic ground state of the ammonia cation NH 3 + has been calculated over a wide range of its vibrational coordinates at the complete-active-space SCF (CASSCF), the multi-reference configuration interaction (MR-CI) and at the coupled-pair-function (CPF) levels of theory. An empirical potential function is fitted to the ab initio points and an additional adjustment of some of the potential function parameters is performed by fitting also to available experimental data within the nonrigid inverter Hamiltonian approximation. Using this adjusted potential function, predictions of unobserved vibrational levels and their rotational structures are made for the NH 3 + and ND 3 + isotopic species. In the calculations of the rotational structures of the bending states the strong perturbation by the ( x- y) Coriolis interaction is taken into account.