OXIDATION-INDUCED IONIZATION AND REACTIONS OF METAL CARBIDE CLUSTERS (NB, ZR, V, TA)

Following our recent report of the oxidation induced formation of Ti8C 12+ (H.T. Deng, K.P. Kerns, and A.W. Castleman, Jr., J. Chem. Phys. 10 4 (1996) 4862), the oxidation induced ionization of niobium and zircon ium carbide clusters are studied using a triple quadrupole mass spectr ometer coupled with a laser induced plasma reaction source. It was fou nd that reactions of both of these neutral carbide clusters with dioxy gen leads to formation of carbide ions. The ion product distributions show that zirconium carbide clusters mainly take the form of Met-Car c ations, but niobium carbide clusters favor a cubic-like crystalline pa ttern. Furthermore, reactions of mass-selected NbxCy+ with dioxygen re sult in a sequential loss of C-2 units from NbxCy+, and leads to forma tion of Nb-x(+) and NbxC+ depending on y being an even or odd number. However, NbxCy+ shows comparably low reactivity towards nitrous oxide through a single oxygen abstraction mechanism. In comparison with the reaction products of VxCy+ with dioxygen, the complementary informatio n obtained in the present study suggests that the C-2 unit is a basic building block for formation of small early transition metal carbide c lusters. The oxidation induced ionization mechanisms are also discusse d in relation with the stability, ionization potentials, and structure s of the clusters. (C) 1997 Elsevier Science B.V.