Full-dimensionality quantum calculations of acetylene/vinylidene isomerization

Abstract

The isomerization of acetylene to vinylidene is examined theoretically in full-dimensionality (six degrees-of-freedom) using a new ab initio potential energy surface [S. Zou and J. M. Bowman, Chem. Phys. Lett. 368, 421(2003)]. Eigenfunctions and eigenvalues of the exact Hamiltonian, for zero total angular momentum, are obtained using a series of novel truncation/recoupling procedures that permits calculations up to very high energies. The Hamiltonian is given in diatom-diatom Jacobi coordinates, with thechoice H₂-C₂ for the two diatoms to exploit the full permutational symmetry of the problem. By examining expectation values of the eigenfunctions, a number of states are clearly identified with vinylidene-like characteristics. Corresponding calculations are also done for C₂D₂. Full dimensional simulations of the photodetachment spectra of [C₂H₂]^- and [C₂D₂]^- are done (within the Franck-Condon approximation) and compared to the experimental ones. The ground vibrational state wavefunction of the anion is obtained using a new force field, based on high quality ab initio calculations, which are also briefly reported.

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