Electron and ion spectroscopy of azobenzene in the valence and core shells

Abstract

Azobenzene is a prototype and building block of a class of molecules of extreme technological interest as molecular photo-switches. We present a joint experimental and theoretical study of its response to irradiation with light across the UV to X-ray spectrum. The study of valence and inner shell photo-ionization and excitation processes, combined with measurement of valence photoelectron-photoion coincidence (PEPICO) and of mass spectra across the core thresholds provides a detailed insight onto the site- and state-selected photo-induced processes. Photo-ionization and excitation measurements are interpreted via the multi-configurational restricted active space self-consistent field (RASSCF) method corrected by second order perturbation theory (RASPT2). Using static modelling, we demonstrate that the carbon and nitrogen K edges of Azobenzene are suitable candidates for exploring its photoinduced dynamics thanks to the transient signals appearing in background-free regions of the NEXAFS and XPS.

Efficient Spin-Adapted Implementation of Multireference Algebraic Diagrammatic Construction Theory. I. Core-Ionized States and X-ray Photoelectron Spectra

“…Figures 3a to 3c show the simulated C K-edge XPS spectra of trans-and cis-azobenzene in the S 0 , nπ*, and ππ* electronic states. For the ground state of trans-isomer, the results of simulations are in an excellent agreement with the experimental spectrum (Figure 3d) measured by Carlini et al 221 In all C Kedge XPS spectra, an intense peak is followed by a feature with weaker intensity that appears as a shoulder in the S 0 spectrum. These two features correspond to the K-edge ionization of C atoms in two distinct chemical environments: 1) ten H-bonded C's and 2) two N-bonded C's.…”

“…Although no experimental TR-XPS studies have been presented to date, the ground-state carbon and nitrogen K-edge XPS spectra of trans-azobenzene in the gas phase have been recently reported. 221 In addition to TR-XPS, time-resolved X-ray absorption spectroscopy has been proposed and theoretically evaluated as a technique for studying azobenzene photoisomerization. 222,223 We performed the MR-ADC(2)-X calculations of XPS spectra at three azobenzene geometries: the equilibrium structures of trans-and cis-isomers and the geometry of minimum energy conical intersection (MECI) between the two lowest-energy singlet states that is believed to be important in photoisomerization (Section 2.3).…”

Fragmentation and charge transfer in cyclic dipeptides with an aromatic side chain induced by VUV radiation

“…Recently, the hemispherical analyzer has been equipped with a position-sensitive detector [22,23] that replaced the original detection system made of six independent channeltrons [21], leading to a significant improvement in terms of efficiency and resolution. A detailed description of the experimental set-up as well as of the experimental procedures can be found in [24].…”

Generalization of One-Center Nonorthogonal Configuration Interaction Singles to Open-Shell Singlet Reference States: Theory and Application to Valence-Core Pump-Probe States in Acetylacetone

“…RASSCF/ RASPT2 have been used to theoretically probe the relaxation pathways of malonaldehyde with XAS, 80 and to predict the NEXAS signatures of the π → π* and N LP → π* states of azobenzene. 81 The third is a generalized-active space-driven similarity renormalization group technique, 82 recently used to explore the NEXAS signatures of three aromatic diradicals. 83 A multireference adaptation to ADC can provide the NEXAS of singlet excited states in theory but that capacity has not been explored yet.…”

“…The second involves carrying out a complete active space (CAS)­SCF calculation, or its dynamically correlated PT2 variant, in conjunction with restricted-active space (RAS) techniques to ensure the proper occupancy of the relevant orbitals: one for the core orbital, one for the valence hole level, and one for the valence particle level. RASSCF/RASPT2 have been used to theoretically probe the relaxation pathways of malonaldehyde with XAS, and to predict the NEXAS signatures of the π → π* and N LP → π* states of azobenzene . The third is a generalized-active space-driven similarity renormalization group technique, recently used to explore the NEXAS signatures of three aromatic diradicals .…”