Differential Relaxation Effects and Multielectron Excitation for Molecularly Chemisorbed CO on Platinum

Abstract

Synchrotron radiation ($h\ensuremath{\nu}=80\ensuremath{-}170$ eV) was used for photoemission studies of CO chemisorption on a Pt crystal. We report the first unambiguous observation of the $3\ensuremath{\sigma}$ molecular level for CO adsorbed on a metal surface and note a relaxation shift 2.4 eV larger for the $3\ensuremath{\sigma}$ than for the $4\ensuremath{\sigma}$ as compared to the $3\ensuremath{\sigma}\ensuremath{-}4\ensuremath{\sigma}$ splitting in the gas phase. Furthermore, we observe energy-loss structure between the $3\ensuremath{\sigma}$ and $4\ensuremath{\sigma}$ levels, reminiscent of the shakeup satellites in transition-metal carbonyls.