New bound electronic states of NH⁺

Ab initio MRD-CI electronic structure calculations were carried out on the NH⁺ cation. A basis set of DZ + POL quality augmented with Rydberg and bond functions was employed, together with an extensive treatment of electron correlation. We find four new bound electronic states of NH⁺, namely, three doublets (²Δ, ²Σ⁺, ²Σ⁺) and one sextet (⁶Π). A fifth bound electronic state, a quartet (⁴Π) that was reported schematically in an early SCF study (Liu, H. P. D.; Verhaegen, G. J Chem Phys 1970, 53(2), 735), is calculated for the first time over a wide range of NH distances. Electronic energies, potential energy curves, and spectroscopic constants are reported for these five states. Vertical and adiabatic excitation and ionization energies are reported, as well as vertical de-excitation energies for emission from the novel states to lower-lying bound states. The potential energy curve of NH²⁺ (X¹Σ⁺) was also calculated to aid in the discussion of a Rydberg bound state of NH⁺. It is hoped that the information reported in this article will be helpful in guiding the experimental detection of these species. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004