Knowledge Bank

As part of a systematic study of triatomic molecules of atmospheric interest, ab initio calculations have been performed on the ground and low-lying excited states of water, nitrous oxide, nitrogen dioxide, carbon dioxide and ozone, as well as their positive and negative ions. Employing a contracted Gaussian type orbital basis set of double-zeta quality, the vertical spectra of the above species were computed using SCF, MCSCF and GI wavefunctions. The methods for constructing the various types of wavefunctions and the effects of electron correlation will be discussed. Specific results for the $O3$, $O3+$, $O3-$ system are presented here and compared with previous theoretical and experimental works.