H-2 ELIMINATION PRODUCTS FROM NEUTRAL ZR PLUS ALKENE REACTIONS IN THEGAS-PHASE

Identification of the metal-containing products of reactions of the ne utral transition metal atom Zr(4d(2)5s(2), F-3) with ethylene and prop ylene is accomplished using one-photon ionization at 157 nm and time-o f-flight mass spectrometry, The reactions proceed in a fast flow react or at 298 K with He/N-2 buffer gas at 0.6 Torr. Mass spectra of the pr oducts of both Zr + C2H4 and Zr + C3H6 indicate that H-2 elimination o ccurs as the primary reaction step. The efficiency of the Zr + C2H4 re action shows that there is no barrier larger than about 2 kcal/mol abo ve reactants along the entire reaction path. This corroborates an earl ier theoretical prediction by Blomberg and Siegbahn of facile H-2 elim ination by ground-state Zr. For the secondary reactions ZrC2H2 + C2H4 and ZrC3H4 + C3H6 and for the reactions ZrO + C2H4 and ZrO + C3H6, mas s spectra again indicate that H-2 elimination occurs. Rate constant me asurements using photoionization detection show that the presence of t he C2H2 and C3H4 ligands enhances the reaction efficiency over that of thr bare Zr atom, while ZrO reacts at essentially the same rate as Zr .