Theoretical investigations on the NH +(X 2Π) ion using coupled-cluster theory in combination with the correlation-consistent quintuple basis set augmented with diffuse functions

Abstract

The coupled-cluster singles-doubles-approximate-triples [CCSD(T)] theory in combination with the series of correlation-consistent basis sets is employed to investigate the equilibrium internuclear separations, harmonic frequencies and potential energy curves of the NH +(X 2Π) ion. The adiabatic potential energy curve obtained at the aug-cc-pV5Z basis set over the internuclear separation range from 0.57 to 24.7 Å is fitted to the analytic Murrell–Sorbie function, which is used to accurately determine the spectroscopic parameters D 0, D e , ω eχ e , α e and B e . The present D 0, D e , R e , ω e , ω eχ e , α e and B e values are of 4.4333 eV, 4.6202 eV, 1.0692 Å, 3049.317 cm −1, 72.522 cm −1, 0.6324 cm −1 and 15.6911 cm −1, respectively, which are in excellent agreement with the available measurements. With the potential obtained at the UCCSD(T)/aug-cc-pV5Z level of theory, a total of 22 vibrational states is predicted by numerically solving the radial Schrödinger equation of nuclear motion when the rotational quantum number J is set to equal zero. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reproduced from the potential when J = 0 for the first time, which are in good agreement with the available experimental data.