Knowledge Bank

The isomerization of acetylene to vinylidene is examined theoretically in full-dimensionality (six degrees-of-freedom) using a new ab initio potential energy $surfacea$. 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 the choice $H2-C2$ 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.