Interface originated modification of electron-vibration coupling in resonant photoelectron spectroscopy

Abstract

We present a comprehensive study of the photon-energy ($h\ensuremath{\nu}$)-dependent line-shape evolution of molecular orbital signals of large $\ensuremath{\pi}$-conjugated molecules by resonant photoelectron spectroscopy (RPES). A comparison to RPES data on small molecules suggests that the excitation into different vibrational levels on the intermediate-state potential energy surface of the electronic excitation is responsible for the observed effect. In this simplified picture of electron-vibration coupling the character of the potential energy surfaces involved in the RPES process determines the line shape of the molecular orbital signal for a particular $h\ensuremath{\nu}$. We use the sensitivity of this effect to probe the influence of different interfaces on the electron-vibration coupling in the investigated systems. The magnitude of the variation in line shape throughout the particular $h\ensuremath{\nu}$ region allows us to reveal significant differences within the physisorptive regime.