CHEMISORPTION OF ETHYLENE ON SI-5(- A THEORETICAL-STUDY() CLUSTER IONS )

The chemisorption of ethylene on Si(5)(+ )clusters is investigated usi ng MP2/6-31G, higher-order correlation and DFT methods. Eight differe nt approaches of C2H4 to the quasi bipyramidal Si-5(+) lead to a numbe r of stable sigma and pi-adducts. It is shown that approach to the mos t stable sigma-adduct (C2H4 di-sigma bonded to Si-5(+)) occurs without or only with a low barrier. The Si-5(+)-C2H4 binding energy, calculat ed to be 1.7 eV, is in reasonably good agreement with experimentally e stimated values of 1.8-2.0 eV. This explains the experimentally observ ed high reactivity of Si-5(+) compared to other silicon clusters, in p articular to the less reactive Si-4(+). (C) 1998 Elsevier Science B.V. All rights reserved.