Studies of molecular photoionization of simple systems by advanced photon sources

This doctorate thesis reports on a variety of experimental investigations aiming to advance the understanding of fundamental processes in molecules and clusters by exploiting the properties of Synchrotron and FEL radiation: photoionization dynamics, double ionization, dissociation and molecular recognition were subject of investigation. The emphasis of the thesis lies on the application of advanced light sources in the study of photoionization processes in simple gas-phase molecules, with particular attention on chiro-optical properties of chiral systems. The valence photoionization dynamics of a chiral molecule, namely the epichlorohydrin molecule, was studied for the first time and a peculiar electron correlation effect was observed. The experimental data were supported by state-of-the-art theoretical calculations. VUV direct double ionization was studied for the methyl oxirane chiral molecule by the use of Photoelectron-Photoion-Photoion Coincidence spectroscopy using synchrotron radiation. The chiral recognition mechanism of 1-methoxy-2-propanol oligomers was studied by FEL based IRMPD-VUV vibrational spectroscopy, a technique that exploits the nature of the photoionization process in order to apply the IRMPD spectroscopy to systems of arbitrary structure. The collaboration between the Sapienza University of Rome, the CNRIOM institute, and the Elettra Instrumentation and Detector Laboratory, has resulted in the development of a position sensitive cross delay line electron detector integrated in an experimental apparatus with the flexibility to perform synchrotron radiation (SR) photoemission experiments on gasphase systems. The improvement of the apparatus detection system has stimulated the collaboration with the Theoretical Chemistry group of the University of Trieste, in a joint experimental and theoretical long-term research activity, whose first part was the study of the photoionization dynamics of the Osmium tetroxide molecule, a highly reactive tetraoxo complex

EXPLORING THE ASYMMETRIC ENVIRONMENT OF VARIOUS CHIRAL CATALYSTS USING A MODIFIED ION-TRAP MASS SPECTROMETER: TOWARDS THE DEVELOPMENT OF A RAPID CHIRAL CATALYST SCREENING METHOD

Since the tragedy of the drug Thalidomide® in the late 1950 to early 1960’s, chirality has been recognized as an important aspect that must be controlled in the drug development process in the pharmaceutical industry. Since then, there has been a considerable movement towards single enantiomer drugs. This demand has presented many challenges for the synthetic organic chemist. Chiral catalysts offer one solution to this problem, as they afford the unique ability to preferentially synthesize one enantiomer. Unfortunately, the design of new chiral catalysts is often empirical, with luck and trial and error necessary due to factors that govern enantioselectivity. Therefore, it would be highly beneficial to develop a method that is capable of screening multiple chiral catalysts early in the catalyst development cycle. Using a modified ion-trap mass spectrometer, the chiral environment of various chiral catalysts may be examined, free from solvent and ion-pairing affects. Thus, the catalyst’s inherent asymmetric environment (enantioselectivity) may be probed using simple chiral molecules, including alcohols, ethers, and epoxides of various steric demands. Using these probes, various C2-symmetric bis-oxazolines and di-imines catalysts were examined. Use of the binaphthyl-based diamine, BINAM, condensed with various 3,5-disubstituted benzaldehydes, provided selectivity close to the privileged catalyst, bis-oxazoline. In general, the chiral probes 1-phenyl-2-propanol, 1-mehtoxyethylbenzene, and styrene oxide offer the best look at the catalyst’s enantioselectivity potential. With the use of the ion-trap mass spectrometer as a mass filter, the purity of the catalyst is not paramount, thus, multiple catalysts may be screened simultaneously, with the constraint that the catalysts must be of different m/z. This thesis presents results found during the exploration of various C2 and C1-symmetric chiral catalysts, in the development of the new chiral screening method utilizing various chiral probes

Synthesis, Characterization, and Investigation of the Catalytic Activity of NiO, CuO, and NiO-CuO Nanoparticles on Silica as Surrogates of Combustion-Generated Nanoparticles

Transition metal oxide nanoparticles contained in fly ash are known to catalyze the formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) during the waste incineration process. The potential catalytic activity of silica-supported NiO, CuO, and NiO-CuO nanoparticles for the formation of PCDD/Fs will be discussed in this dissertation. The successful synthesis of silica-supported NiO, CuO, and NiO-CuO nanoparticles as surrogates of combustion-generated nanoparticles was important to this study. The synthesis was followed by the characterization of the nanoparticle surrogates by X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). Finally, the catalytic activity of these nanoparticle surrogates for the formation of PCDD/Fs was investigated. Silica-supported metal oxide nanoparticles were prepared by wetness impregnation of metal ionƒ{dendrimer complexes (WI-D) and wetness impregnation of metal ion solutions (WI-M), both followed by oxidative thermal treatment (calcination). NiO nanoparticles with low size dispersity (14%) and an average diameter of 3.6 ¡Ó 0.5 nm were formed by the WI-D method followed by calcination at 500 „aC for 5 h. NiO nanoparticles prepared by the WI-M method showed of low size dispersity (14%) and an average diameter 2.9 ¡Ó 0.4 nm followed by calcination at 500 „aC for 5 h. For the first time, mixed NiO-CuO nanoparticles were synthesized with the ability to control their Ni:Cu (1:1, 1:3, 1:10, 10:1, and 3:1) molar composition by altering the amounts of metal ions in the starting solutions. Catalytic activity of NiO, CuO, and NiO-CuO nanoparticles was investigated by reacting 2-monochlorophenol (2-MCP)ƒ{a known PCDD/Fs precursorƒ{on their surface at cool-zone temperatures of waste incinerators (300¡V500 „aC with 50 „aC intervals). Results indicated nearly 85% of the 2-MCP was reacted at 300 „aC, while close to 100% conversion was achieved for 2-MCP at temperatures above 450 „aC. It is proposed that the reactions associated with PCDD/Fs formation were initiated by binding of 2-MCP to the metal-oxide sites on the silica support, followed by formation of surface-bound chlorinated phenol molecule. PCDD/Fs yields as a function of reaction temperature and the nature of the catalyst (NiO, CuO and NiO-CuO) will be discussed

Summaries of FY 1997 Research in the Chemical Sciences

The objective of this program is to expand, through support of basic research, knowledge of various areas of chemistry, physics and chemical engineering with a goal of contributing to new or improved processes for developing and using domestic energy resources in an efficient and environmentally sound manner. Each team of the Division of Chemical Sciences, Fundamental Interactions and Molecular Processes, is divided into programs that cover the various disciplines. Disciplinary areas where research is supported include atomic, molecular, and optical physics; physical, inorganic, and organic chemistry; chemical energy, chemical physics; photochemistry; radiation chemistry; analytical chemistry; separations science; heavy element chemistry; chemical engineering sciences; and advanced battery research. However, traditional disciplinary boundaries should not be considered barriers, and multi-disciplinary efforts are encouraged. In addition, the program supports several major scientific user facilities. The following summaries describe the programs

Confining isolated atoms and clusters in crystalline porous materials for catalysis

[EN] Structure-reactivity relationships for nanoparticle-based catalysts have been greatly influenced by the study of catalytic materials with either supported isolated metal atoms or metal clusters comprising a few atoms. The stability of these metal species is a key challenge because they can sinter into large nanoparticles under harsh reaction conditions. However, stability can be achieved by confining the nanoparticles in crystalline porous materials (such as zeolites and metal-organic frameworks). More importantly, the interaction between the metal species and the porous framework may modulate the geometric and electronic structures of the subnanometric metal species, especially for metal clusters. This confinement effect can induce shape-selective catalysis or different chemoselectivity from that of metal atoms supported on open-structure solid carriers. In this Review, we discuss the structural features, synthesis methodologies, characterization techniques and catalytic applications of subnanometric species confined in zeolites and metal-organic frameworks. We make a critical comparison between confined and non-confined isolated atoms and metal clusters, and provide future perspectives for the field.We are grateful for financial support from the European Research Council (grant ERC-AdG-2014-671093, SynCatMatch) and the Spanish Government through the Severo Ochoa Program (SEV-2016-0683).Liu, L.; Corma Canós, A. (2021). Confining isolated atoms and clusters in crystalline porous materials for catalysis. Nature Reviews Materials. 6(3):244-263. https://doi.org/10.1038/s41578-020-00250-32442636

Molecular aggregation of thiols and alcohols: study of non-covalent interactions by microwave spectroscopy

El estudio y comprensión de las interacciones no covalentes a nivel molecular es un campo que está en continuo desarrollo y cobra vital importancia para determinar el comportamiento estructural de muchas moléculas de interés químico, tecnológico o biológico. En esta tésis doctoral se han analizado las interacciones intermoleculares implicadas en la formación de agregados moleculares neutros, tanto dímeros como productos de microsolvatación, en fase gas. Los complejos intermoleculares se han generado mediante expansiones supersónicas pulsadas, caracterizándose posteriormente mediante espectroscopía de rotación. Este trabajo ha utilizado dos técnicas espectroscópicas, incluyendo un espectrómetro de microondas con transformada de Fourier (FTMW) de tipo Balle-Flygare en el rango de frecuencias 8-20 GHz, y un espectrómetro de transformada de Fourier de banda ancha con excitación multifrecuencia (CP-FTMW) cubriendo el rango espectral de 2-8 GHz. Los complejos intermoleculares estudiados han incluido moléculas con grupos alcohol y/o tiol, con objeto de analizar las diferencias entre las interacciones intermoleculares que implican átomos de oxígeno o azufre, en especial el enlace de hidrógeno. Se han estudiado moléculas incluyendo tanto sistemas cíclicos alifáticos (ciclohexanol, ciclohexanotiol) como aromáticos (furfuril alcohol, furfuril mercaptano, tienil alcohol, tienil mercaptano). Los enlaces de hidrógeno analizados han comprendido especialmente interacciones de tipo O-H···O, O-H···S y S-H···S. La formación de los complejos intermoleculares ha revelado en algunos de ellos una gran variedad conformacional, como la observación de seis isómeros del dímero de ciclohexanol. En el caso de los monohidratos se han observado en algunos casos desdoblamientos asociados a movimientos internos de gran amplitud, como la rotación de la molécula de agua en los monohidratos de ciclohexanol y tienil mercaptano. En los casos de moléculas quirales la dimerización ha permitido observar la estabilidad relativa de los diastereoisómeros homo o heteroquirales. El estudio experimental se ha completado con diferentes cálculos teóricos de orbitales moleculares, en especial teoría del funcional de la densidad, a fin de caracterizar las interacciones estructuralmente, energéticamente y mediante análisis topológico de la densidad electrónica. El conjunto de datos experimentales y teóricos permite aumentar la información existente sobre enlaces de hidrógeno con átomos de azufre, generalmente poco estudiados, y su comparación con los análogos oxigenados.The study and understanding of non-covalent interactions at molecular level is a field in continuous development and essential to determine the structural behavior of many molecules of chemical, technological or biological interest. In this PhD thesis, the intermolecular interactions involved in the formation of neutral molecular aggregates, both dimers and microsolvation products, have been analyzed in the gas phase. The intermolecular complexes were generated by pulsed supersonic expansions, and later characterized by rotational spectroscopy. This work has used two spectroscopic techniques, including a Balle-Flygare Fourier-Transform Microwave (FTMW) spectrometer in the 8-20 GHz frequency range, and a broadband Chirped-Pulse Fourier Transform Microwave (CP-FTMW) spectrometer covering the 2-8GHz spectral range. The intermolecular complexes studied have included molecules with alcohol and / or thiol groups, in order to analyze the differences between the intermolecular interactions involving oxygen or sulfur atoms, especially hydrogen bonds. Molecules that comprise both aliphatic (cyclohexanol) and aromatic (furfuryl alcohol, furfuryl mercaptan, thenyl alcohol, thenyl mercaptan) ring systems have been studied. The analyzed hydrogen bonds included especially O-H···O, O-H···S and S-H···S interactions. The formation of intermolecular complexes has revealed a great conformational diversity in some of them, such as the observation of six isomers of the cyclohexanol dimer. With regard to the monohydrates, tunnelling splittings associated with internal large amplitude motions have been observed in some cases, such as the rotation of the water molecule in the monohydrates of cyclohexanol, thenyl alcohol and thenyl mercaptan. In the case of chiral molecules, dimerization has made it possible to observe the relative stability of homo- or heterochiral diastereoisomers. The experimental study has been supported by different theoretical molecular orbital calculations, in particular Density Functional Theory (DFT) calculations, in order to characterize the interactions structurally, energetically and by a topological analysis of electron density. The set of experimental and theoretical data will advance the existing information on hydrogen bonds involving sulfur atoms, generally scarcely studied, and their comparison with the oxygenated analogues.Departamento de Química Física y Química InorgánicaDoctorado en Físic