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

Azobenzene is a prototype and a 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 and mass spectra across the core thresholds provides a detailed insight into 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 method corrected by second order perturbation theory. Using static modeling, 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

Roadmap on dynamics of molecules and clusters in the gas phase

This roadmap article highlights recent advances, challenges and future prospects in studies of the dynamics of molecules and clusters in the gas phase. It comprises nineteen contributions by scientists with leading expertise in complementary experimental and theoretical techniques to probe the dynamics on timescales spanning twenty order of magnitudes, from attoseconds to minutes and beyond, and for systems ranging in complexity from the smallest (diatomic) molecules to clusters and nanoparticles. Combining some of these techniques opens up new avenues to unravel hitherto unexplored reaction pathways and mechanisms, and to establish their significance in, e.g. radiotherapy and radiation damage on the nanoscale, astrophysics, astrochemistry and atmospheric science

An electrospray ionisation apparatus for gas phase study of biomolecules

International audienceSynopsis A set-up to study large biomolecules in the gas phase based on an ElectroSpray Ionisation source has been installed at CNR-ISM in Rome, and it is currently under commissioning. Accurate ion optics simulation provide crucial feedback in the understanding and optimisation of its performance

Insights into 2- and 4(5)-nitroimidazole decomposition into relevant ions and molecules induced by VUV ionization

Nitromidazoles are relevant compounds of multidisciplinary interest, and knowledge of their physical-chemical parameters as well as their decomposition under photon irradiation is needed. Here we report an experimental and theoretical study of the mechanisms of VUV photofragmentation of 2- and 4(5)-nitromidazoles, compounds used as radiosensitizers in conjunction with radiotherapy as well as high-energy density materials. Photoelectron-photoion coincidence experiments, measurements of the appearance energies of the most important ionic fragments, density functional theory, and single-point coupled cluster calculations have been used to provide an overall insight into the energetics and structure of the different ionic/neutral products of the fragmentation processes. The results show that these compounds can be an efficient source of relevant CO, HCN, NO, and NO2molecules and produce ions of particular astrophysical interest, like the isomers of azirinyl cation (m/z 40), predicted to exist in the interstellar medium, and protonated hydrogen cyanide (m/z 28)

VUV Photofragmentation of Chloroiodomethane: The Iso-CH2ICl and Iso-CH2ClI Radical Cation Formation

Dihalomethanes XCH2Y (X and Y= F, Cl, Br and I) are a class of compounds involved in several processes leading to the release of halogen atoms, ozone consumption and aerosol particle formation. Neutral dihalomethanes have been largely studied, but chemical physics properties and processes involving their radical ions, like the pathways of their decomposition, have not been completely investigated. In this work the photodissociation dynamics of the ClCH2I molecule has been explored in the photon energy range 9-21 eV using both VUV rare gas discharge lamps and synchrotron radiation. The experiments show that among the different fragment ions, CH2I+ and CH2Cl+, which correspond to the Cl- and I-losses, respectively, play a dominant role. The experimental ionization energy of ClCH2I and the appearance energies of the CH2I+ and CH2Cl+ ions are in agreement with the theoretical results obtained at the MP2/CCSD(T) level of theory. Computational investigations have been also performed to study the isomerization of geminal [ClCH2I].+ into the iso-chloroiodomethane isomers: [CH2I-Cl].+ and [CH2Cl-I].+

On the mechanisms of formation and decomposition of peptide bonds

International audienceSynopsis The electronic structure and the fragmentation dynamics of a series of isolated cyclic-dipeptides (cyclo-Ala-Ala; cyclo-Gly-Ala; cyclo-Gly-Gly) have been studied by mass spectrometry, photoemission and photoelectron-photoion coincidence spectroscopy

Insights into 2- and 4(5)-Nitroimidazole Decomposition into Relevant Ions and Molecules Induced by VUV Ionization

Nitromidazoles are relevant compounds of multidisciplinary interest, and knowledge of their physical–chemical parameters as well as their decomposition under photon irradiation is needed. Here we report an experimental and theoretical study of the mechanisms of VUV photofragmentation of 2- and 4(5)-nitromidazoles, compounds used as radiosensitizers in conjunction with radiotherapy as well as high-energy density materials. Photoelectron–photoion coincidence experiments, measurements of the appearance energies of the most important ionic fragments, density functional theory, and single-point coupled cluster calculations have been used to provide an overall insight into the energetics and structure of the different ionic/neutral products of the fragmentation processes. The results show that these compounds can be an efficient source of relevant CO, HCN, NO, and NO₂ molecules and produce ions of particular astrophysical interest, like the isomers of azirinyl cation (<i>m</i>/<i>z</i> 40), predicted to exist in the interstellar medium, and protonated hydrogen cyanide (<i>m</i>/<i>z</i> 28)