The XPS peak structure of condensed aromatic anhydrides and imides

TL;DR

This study analyzes the complex XPS peak structures of aromatic anhydrides and imides, revealing the significant role of shake-up satellites and providing a semiempirical model to interpret electronic charge transfer processes.

Contribution

The paper introduces a semiempirical SDCI calculation method that accurately reproduces experimental XPS spectra by including intermolecular shake-up excitations, advancing understanding of electronic interactions in organic molecules.

Findings

Shake-up satellites significantly influence XPS peak structures.

Intermolecular excitations are crucial for accurate spectral modeling.

Structural modifications affect charge transfer and satellite intensities.

Abstract

Photoelectron spectra of aromatic anhydrides and imides like PTCDA (perylene-tetracarboxylic dianhydride), PTCDI (perylene-tetracarboxylic diimide), and NDCA (naphthalene-dicarboxylic anhydride) on smooth single crystal surfaces show complex double peak structures in both the O1s and the anhydride C1s range. The peak intensity ratios cannot be simply explained by different chemical states of the atoms but are strongly influenced by intense shake-up satellites. Semiempirical SDCI calculations can quantitatively reproduce the experimental spectra of multilayers, provided that not only intramolecular but also intermolecular shake-up excitations are taken into account. These calculations give further insight into the process of electronic charge transfers in large organic molecules and molecular films. A variation of the molecular structure by reducing the size of the aromatic part (NDCA instead of PTCDA) or by using different functional groups (PTCDI instead of PTCDA) leads to a reduced donor/acceptor strength and hence to drastically reduced satellite intensities.