The orientation and symmetry of adsorbed cyclopropane on Ru(001) measured by off specular high resolution electron energy loss spectroscopy and angular resolved photoelectron spectroscopy

Abstract

In order to determine the orientation and symmetry of cyclopropane adsorbed at 95 K on Ru(001) at and below saturation surface coverage, we have combined i n s i t u high resolution electron energy loss spectroscopy(EELS) and angular resolved UV‐photoelectron spectroscopy (ARUPS). Both the vibrational and the photoelectron spectra show that the molecule adsorbs associatively with neither an opening of the carbon ring nor an abstraction of hydrogen atoms from the ring. The dipole activity of the ring modes ν10(1010 cm−1) and ν11 (880 cm−1) in EELS and the polar angular distribution in photoemission of the 1a 2\, 3a 1′, and 1e\ molecular orbitals suggest C s (σ v ) symmetry of the admolecule. This type of reduced symmetry can result from an orientation of the molecule in which one C–C bond, but not the entire carbon ring, is parallel to the surface. Both the orientation and the symmetry of the admolecule are discussed in relation to a tentative bonding picture assuming a weak interaction between the delocalized ’’external’’ σCC orbital (mainly 3e′) of the molecule and the metal surface.