Matrix infrared spectra of dihydrido cyclic and trihydrido ethynyl products from reactions of Th and U atoms with ethylene molecules.

Reactions of laser-ablated thorium and uranium atoms with ethylene isotopomers have been carried out and the primary products identified in the matrix IR spectra. The dihydrido cyclic and trihydrido ethynyl products (MH(2)-C(2)H(2) and MH(3)CCH) are identified from the matrix spectra of both Th and U, whereas the insertion product absorption is observed only in the U spectra. The present results indicate that C-H insertion and following H migration from C to M also occur in reaction of the actinides with ethylene. Formation of the trihydrido ethynyl products is parallel to the previous results of group 4 metals. Metal hydride (MH(x)) absorptions are not observed in the infrared spectra, suggesting that the H(2) elimination from the dihydrido cyclic intermediate is relatively slow. Density functional theory calculations reproduce the vibrational characteristics of the identified products and the relative stabilities. The cyclic triangular ThH(2)-C(2)H(2) system with two pi electrons is aromatic, which contributes to the unique stability of this thorium dihydrido cyclic product.