Theoretical investigations on the NH+(X2Î ) ion using coupled-cluster theory in combination with the correlation-consistent quintuple basis set augmented with diffuse functions

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+(X2Π) 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 D0, De, ωeχe, αe and Be. The present D0, De, Re, ωe, ωeχe, αe and Be 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.