Knowledge Bank

Purely {\em ab initio} CCSD(T) quartic force fields have been determined for the lowest triplet and singlet states of HO$\mathrm{2+}$ ion with TZ-,QZ- and 5Z-level one-particle basis sets. After extrapolating to complete basis-set limit, small correction terms have now been incorporated, including core-correlation, scalar relativistic, and others. Anharmonic vibrational fundamentals and ro-vibrational spectroscopic constants are computed with perturbational and variational methods. Our best computed force field should give fundamentals to within $\pm 5$ cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$. In this talk we will present the procedure details and compare our results with previous work on this ion. Effects of small corrections and benchmark results on H$2$O will also be discussed.