Theoretical investigation of excited and Rydberg states of imidogen radical NH: Potential energy curves, spectroscopic constants, and dipole moment functions

A search is conducted for the calculation of potential energy curves (PECs), spectroscopic constants, and dipole moment functions for excited and Rydberg states of imidogen radical NH, with a particular emphasis on the Rydberg states arising from 3s configuration of nitrogen and 2s and 2p configurations of hydrogen. A range of about 11 eV above the electronic ground state X (3)Sigma(-) atomic separation limit which corresponds to the first eight asymptotes of dissociation is spanned. Computations are carried out at the internally contracted multireference singles plus doubles configuration interaction level of theory, including the Davidson correction to account for quadruple excitations. The Gaussian basis set used has been modified from a standard basis to give a balanced description of valence-Rydberg interactions. States of (1)Sigma(-), (1)Pi, (1)Delta, (3)Sigma(-), (3)Pi, (3)Delta, and (5)Sigma(-) symmetries are computed accurately in the range of energy investigated. PECs of the three lowest (5)Pi states are obtained for the first time. Our spectroscopic constants show good agreement with experimental data in comparison with other theoretical studies reported in the literature. A discussion on the variations of dipole moment functions helps to understand the strong interactions between excited and Rydberg states as well as the avoided crossings. The present study may be of great practical interest for investigations in astrophysical research as well as in laboratory experiments. (c) 2007 American Institute of Physics.