A comprehensive photoabsorption, photoionization, and shake-up excitation study of the C 1s cross section of benzene

Abstract

The absolute photoabsorption cross section of benzene (C6H6), encompassing the C 1s−1 π*e2u resonance, the C 1s threshold, the satellite thresholds, and extending up to 800 eV, has been measured using synchrotron radiation. Measurements of the discrete absorption structure from below the C 1s ionization threshold have been performed at high resolution. In order to unambiguously assign all structure present in the photoabsorption cross section, C 1s photoelectron spectra were measured from the C 1s threshold region up to 350 eV along with satellite spectra. The C 1s−1 single-hole and the satellite cross sections have been derived in absolute units, and their angular distributions have been determined. Resonant and normal Auger spectra were taken on the main features of the photoabsorption and single-hole cross sections. From the best resolved photoelectron spectra the underlying structure in the asymmetric benzene photoelectron peak can be partly disentangled. The experimental data show that at least two vibrational modes play a role in the C 1s photoelectron spectrum. The behavior of the investigated shake-up structure closely resembles that of ethene and ethyne, where the satellite bands due to π→π* excitations gain intensity towards threshold, an observation which may be attributed to conjugate shake-up processes. These processes lead to a significant contribution of the satellite intensity to the production of the absorption features traditionally assigned to the carbon shape resonances in benzene. An EXAFS analysis of the wide range oscillations present on the photoabsorption cross section has been performed, and reveals the C–C nearest-neighbor distance.

Destruction and multiple ionization of PAHs by X-rays in circumnuclear regions of AGNs

“…However, to the best of our knowledge, there is neither experimental nor theoretical data on the absolute photoabsorption cross section of PAHs at 2500 eV. Even for benzene, which is the building block of PAHs and one of the most emblematic molecular systems, such measurements have only been made up to 800 eV (Rennie et al 2000).…”

“…Such estimates were based on PAH experiments with lower energy photons, up to the VUV range (Leach et al 1989a,b;Jochims et al 1994Jochims et al , 1996Jochims et al , 1999, and on the photoabsorption profile of the C atom in a photon energy range up to 30 keV (Henke et al 1982(Henke et al , 1993. In addition, the interaction of PAHs and their precursors with photons around the C1s→ π* resonance (285 eV) has been explored by several authors (Rennie et al 2000;Boechat-Roberty et al 2009;Reitsma et al 2014Reitsma et al , 2015Monfredini et al 2016;Quitián-Lara et al 2018). However, there is still a lack of data when it comes to investigating the effects of keV photons on these astrophysically relevant molecules.…”

Nitrogen substitution impacts organic-metal interface energetics

“…5(b)]. In the multilayer regime, the peak shifts to 399.3 eV BE, and a second peak at 401.2 eV BE becomes visible, which is ascribed to a shake-up excitation [62,63]. The C1s multilayer peak shifts by ∼0.3 eV to higher BEs compared to the monolayer.…”

Time dependent density functional theory study of the near-edge x-ray absorption fine structure of benzene in gas phase and on metal surfaces

“…1,12,[40][41][42][43][44][45] In experiment four prominent bands are observed below the ionization threshold. 43 These are referred to as A, B, C and D, and occur at 285.2, 287.2, 287.9 and 289.2 eV, respectively. Peak A is the most intense peak and is assigned to excitation to e 2u orbitals, which correspond to the lowest * orbitals.…”