Saturated hydrocarbons on a Cu surface: a new type of chemical interaction?

Ab initio Hartree-Fock (HF) calculations for cyclopropane adsorbed on a Cu- cluster reveal that the so-called M*-resonance seen in X-ray absorption (NE XAFS)-spectra for saturated hydrocarbons adsorbed on metal surfaces is due to a strong electronic mixing between the metal and the molecule. Since thi s type of chemical interaction is unexpected and has not been observed prev iously the different types of interactions were carefully analyzed. In addi tion to the importance of correlation effects the results reveal that a sma ll but significant interaction is due to a charge-donation from the metal s tates to the molecule, most likely to states of Rydberg character. (C) 2000 Elsevier Science B.V. All rights reserved.