We report the results of extensive configuration interaction studies on 16 excited states of water. These states can be accurately described as corresponding to excitation from one of the highest two molecular orbitals (1b1 or 3a1) of the ground state into either the 3s or one of the three 3p Rydberg orbitals. The results provide the most accurate and consistent treatment of these states to date (within 0.1 eV for all known transitions) and form a reliable basis for the assignment of the photon and electron impact spectra of H2O.
A b initio calculations using the generalized valence bond (GVB) method have been carried out for the lowest triplet and singlet states of O2 at internuclear distances (R) between 2a0 and 6a0. In contrast to other orbital descriptions, GVB leads correctly to ground state oxygen atoms as the bond length is increased to infinity. This proper behavior requires optimization of the spatial orbitals themselves and of the permutational coupling between them as well. Analysis of the results as a function of R is straightforward. Constructing a simple configuration interaction (CI) wavefunction using the GVB orbitals leads to excellent potential curves, accounting for 94% of the bond dissociation energy. The calculated adiabatic separation of the singlet and triplet states is 1.09 eV, which is 0.11 eV above the experimental Te.
Barrier heights and transition state geometries have been calculated for the reaction Oep) + H 2 ->OH + H using large scale POL·CI wave functions (based on GVB wave functions using basis sets of up to triple zeta valence plus double zeta polarization quality). A detailed study was made of the effects on the calculated barrier height and saddle point geometry of (i) basis set, (ii) choice of orbitals, and (iii) choice of reference configurations. Calculations using a [4s3p2d/3s2p) basis lead to a collinear saddle point with r HH = 0.92 A and rOH = 1.23 A with a corresponding barrier height of 12.5 kcaI!mole. There are two surfaces which connect the reactants with the products: one of 3A' symmetry and one of JA" symmetry (these correspond to the two degenerate components of the 311 state in collinear geometries). In the transition state region, the 3 A' surface has a steeper bending curve than the JA" surface leading to significantly different reaction rates on the two surfaces.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.