Spectroscopic quality ab initio potential curves for CH, NH, OH and HF. A convergence study

A calibration study has been carried out on the ground-state potential curves of CH, NH, OH and HF. Using uncontracted spdfgh or spdfghi basis sets in conjunction with treatments of core correlation and imperfections in the CCSD(T) method, re and ωe of the first-row diatomic hydrides can on average be reproduced to within 0.0002 Å and 1 cm−1, respectively, as can the first 4–6 vibrational quanta. The CCSD(T) basis set limit systematically overestimates ωe by 4–9 cm−1 and underestimates re by 0.0003–0.0006 Å. Higher anharmonicities exhibit pronounced basis set sensitivity, which is markedly reduced upon uncontracting the basis set.