Theoretical Study of the Spectroscopy and Dynamics of the Vinylidene-acetylene Iso- Merization

The results of a 5D ab initio quantum dynamical study of the vinylidene acetylene isomerization reaction are presented. The study is based on a new ab initio potential energy surface for the planar system, obtained with the CCSD(T) method and the cc-pVTZ basis set. The dynamics is studied with grid methods, using 4-atom Jacobi-like coordinates and wave packet propagation techniques. The results of a 3D treatment, including the 2 angular degrees of freedom and the C-C stretching mode, have been reported earlier in the literature. Including all (planar) degrees of freedom, the experimental photodetachment spectrum of Lineberger and coworkers is very well reproduced. Furthermore, lifetimes for broadband excitation and for individual vibrational levels of vinylidene have been computed, the latter with the aid of filter diagonalization techniques. The lifetimes are 2-3 orders of magnitude longer that previously believed, indicating a surprising stability of this reactive intermediate. Similar results have been obtained for the deuterated species, D CC supporting the above conclusions.