Isomerization Reaction Surfaces: Quantum Mechanical Studies of Triplet C2H2, Singlet AlHO and Singlet C2H2O

High-level ab initio molecular electronic structure theory has been utilized to investigate specific isomerization reaction surfaces including the triplet acetylene and vinylidene potential energy PE hypersurface, the X-tilde HAlO and AlOH PE hypersurface and the X-tilde oxirene potential energy minima. Basis sets as large as triple zeta plus two sets of polarization functions augmented with higher angular momentum functions TZ2df,2pd have been utilized in conjunction with correlated methods as sophisticated as the coupled cluster approach including all single, double and perturbative triple excitations CCSDT. Of particular interest are predictions of the activation energies, zero-point vibrational energy ZPVE corrected barriers for rearrangement, of a-tilde 3B2 vinylidene to b-tilde 3Bu trans-bent acetylene and of cis-bent a 3B2 acetylene to trans-bent b-tilde 3Bu acetylene. The physical properties of a-tilde 3B2 vinylidene, including the dipole moment, harmonic vibrational frequencies and the infrared intensities, have also been reported. The activation energy and Delta E from X-tilde HAlO to X-tilde AlOH is predicted. Some molecular properties of HAlO and AlOH in their equilibrium geometries useful for experimental identification purposes are also given.