Implementace techniky iontového zobrazování ve fotodisociačním experimentu s volnými molekulami, klastry a nanočásticemi ve vakuu

Název práce: Implementace techniky iontového zobrazování ve fotodisociačním experimentu s volnými molekulami, klastry a nano částicemi ve vakuu Autor: Jaroslav Kočišek Katedra: Katedra fyziky povrchů a plazmatu Vedoucí disertační práce: Mgr. Michal Fárník, PhD., DSc., Ústav fyzikální chemie J. Heyrovského, AV ČR, v.v.i. Abstrakt: Experimentálna práca sa zaoberá implementáciou nových techník do oblasti štúdia klastrov a nanočastíc v molekulových zväzkoch. V rámci práce bol otestovaný systém kombinujúci pulzný molekulový zdroj klastrov s technikou iónového zobrazovania v konfigurácii mapovania rýchlostí. Následne bola rovnaká metóda implementovaná spolu s novým hmotnostným spektrometrom na zariade- nie s molekulovým zväzkom veľkostne selektovaných klastrov. Nové metódy boli použité na štúdium vplyvu prostredia na foto a elektrónmi indukované reakcie klastrov. Medzi najdôležitejšie výsledky patrí ukázanie vplyvu expanzných pod- mienok na štruktúru formovaných klastrov HBr a C2H2. Výsledky experimentov s molekulami HNO3 a CF2Cl2 sú potom dôležité pre pochopenie heterogénnych procesov v stratosfére. Klíčová slova: iontové zobrazování, hmotnostní spektrometrie, molekulové svazky, fotchemie, nanočásticeTitle: Implementation of ion imaging technique in experiments with free molecules, clusters and nanoparticles Author: Jaroslav Kočišek Department: Department of Surface and Plasma Science Supervisor: Mgr. Michal Fárník, PhD., DSc., Ústav fyzikální chemie J. Hey- rovského, AV ČR, v.v.i. Abstract: The experimental work is focused on implementation of novel tech- niques to study clusters and nanoparticles in molecular beams. A new exper- imental system was tested, which combines the technique of velocity map ion imaging with pulsed molecular beam source. The same method and new mass spectrometer were implemented on the apparatus with molecular beam of size selected clusters. The new methods were used to study environmental effects on photo and electron induced chemistry. The most important results concerns on influence of expansion conditions on the structure of formed neutral clusters of HBr and C2H2. Results of experiments with HNO3 and CF2Cl2 molecules are then crucial for understanding heterogeneous processes in the Stratosphere. Keywords: ion imaging, mass spectrometry, molecular beams, photochemistry, nanoparticlesMatematicko-fyzikální fakultaFaculty of Mathematics and Physic

Ring formation and hydration effects in electron attachment to misonidazole

This research was funded by CZECH SCIENCE FOUNDATION grant number 19-01159S; Czech Ministry of Education Youth and Sports via OP RDE Grant no. CZ.02.2.69/0.0/16_027/0008355; S.D. acknowledges funding from the FWF, Vienna (P30332).We study the reactivity of misonidazole with low-energy electrons in a water environment combining experiment and theoretical modelling. The environment is modelled by sequential hydration of misonidazole clusters in vacuum. The well-defined experimental conditions enable computational modeling of the observed reactions. While the NO- 2 dissociative electron attachment channel is suppressed, as also observed previously for other molecules, the OH- channel remains open. Such behavior is enabled by the high hydration energy of OH- and ring formation in the neutral radical co-fragment. These observations help to understand the mechanism of bio-reductive drug action. Electron-induced formation of covalent bonds is then important not only for biological processes but may find applications also in technology.publishersversionpublishe

Implementation of ion imaging technique in experiments with free molecules, clusters and nanoparticles

Title: Implementation of ion imaging technique in experiments with free molecules, clusters and nanoparticles Author: Jaroslav Kočišek Department: Department of Surface and Plasma Science Supervisor: Mgr. Michal Fárník, PhD., DSc., Ústav fyzikální chemie J. Hey- rovského, AV ČR, v.v.i. Abstract: The experimental work is focused on implementation of novel tech- niques to study clusters and nanoparticles in molecular beams. A new exper- imental system was tested, which combines the technique of velocity map ion imaging with pulsed molecular beam source. The same method and new mass spectrometer were implemented on the apparatus with molecular beam of size selected clusters. The new methods were used to study environmental effects on photo and electron induced chemistry. The most important results concerns on influence of expansion conditions on the structure of formed neutral clusters of HBr and C2H2. Results of experiments with HNO3 and CF2Cl2 molecules are then crucial for understanding heterogeneous processes in the Stratosphere. Keywords: ion imaging, mass spectrometry, molecular beams, photochemistry, nanoparticle

Implementation of ion imaging technique in experiments with free molecules, clusters and nanoparticles

Title: Implementation of ion imaging technique in experiments with free molecules, clusters and nanoparticles Author: Jaroslav Kočišek Department: Department of Surface and Plasma Science Supervisor: Mgr. Michal Fárník, PhD., DSc., Ústav fyzikální chemie J. Hey- rovského, AV ČR, v.v.i. Abstract: The experimental work is focused on implementation of novel tech- niques to study clusters and nanoparticles in molecular beams. A new exper- imental system was tested, which combines the technique of velocity map ion imaging with pulsed molecular beam source. The same method and new mass spectrometer were implemented on the apparatus with molecular beam of size selected clusters. The new methods were used to study environmental effects on photo and electron induced chemistry. The most important results concerns on influence of expansion conditions on the structure of formed neutral clusters of HBr and C2H2. Results of experiments with HNO3 and CF2Cl2 molecules are then crucial for understanding heterogeneous processes in the Stratosphere. Keywords: ion imaging, mass spectrometry, molecular beams, photochemistry, nanoparticle

Electron attachment to hexafluoropropylene oxide (HFPO)

We probe the electron attachment in hexafluoropropylene oxide, C3F6O, a gas widely used in plasma technologies. We determine the absolute electron attachment cross section using two completely different experimental approaches: (i) a crossed-beam experiment at single collision conditions (local pressures of 5x10-4 mbar) and (ii) a pulsed Townsend experiment at pressures of 20 - 100 mbar. In the later method, the cross sections are unfolded from the electron attachment rate coefficients. The cross sections derived independently by the two methods are in very good agreement. We additionally discuss the dissociative electron attachment fragmentation patterns and their role in the radical production in industrial HFPO plasmas.ISSN:0021-9606ISSN:1089-769

Effect of cluster environment on the electron attachment to 2-nitrophenol

Effect of cluster environment on the electron attachment to 2-nitrophenol (2NP) is studied in homogeneous 2NP clusters and heterogeneous clusters of 2NP, argon and water. The cluster environment significantly reduces fragmentation of 2NP after electron attachment. Parent cluster anions 2NPn- are primary reaction products in both, homogeneous and heterogeneous clusters. Non-dissociative electron attachment to homogeneous clusters proceeds at low energies <2 eV, presumably via dipole-supported states. In heterogeneous clusters, the interaction with low energy (<2 eV) electrons is shielded by the solvent. Surprisingly, the energetic threshold for the electron attachment rises with the number (n) of 2NP molecules in the cluster (2NP)n-. This rise can be either due to a strong change of the 2NP conformation induced by the cluster environment or due to the the competition with electron autodetachment after proton transfer that has been first observed by Allan in the formic acid dimer [M. Allan, Phys. Rev. Lett. 98, 123201 (2007)]. We observe the same threshold rise for complex Arm·(2NP)n- and H2O·(2NP)n- anions. This indicates that the electron attachment to 2-nitrophenol in cluster environment is more influenced by the solute − solute interaction compared to the solute − solvent interaction

Suppression of low-energy dissociative electron attachment in Fe(CO)5 upon clustering

In this work, we probe anion production upon electron interaction with Fe(CO)5 clusters using two complementary cluster-beam setups. We have identified two mechanisms that lead to synthesis of complex anions with mixed Fe/CO composition. These two mechanisms are operative in distinct electron energy ranges. It is shown that the elementary decomposition mechanism that has received perhaps the most attention in recent years (i.e., dissociative electron attachment at energies close to 0 eV) becomes suppressed upon increasing aggregation of iron pentacarbonyl. We attribute this suppression to the electrostatic shielding of a long-range interaction that strongly enhances the dissociative electron attachment in isolated Fe(CO)5

Dissociative attachment of low-energy electrons to acetonitrile

We experimentally probed the low-energy electron-induced dissociation of acetonitrile and acetonitrile-$$\hbox {d}_3$$ and performed density functional theory calculations to support the experimental results. The previous studies on electron attachment to acetonitrile presented a number of contradictory findings, which we aimed to resolve in the present study. We observed the formation of $$\hbox {H}^-$$, $$\hbox {CH}_2^-$$, $$\hbox {CH}_3^-$$, $$\hbox {CN}^-$$, $$\hbox {CCN}^-$$, $$\hbox {CHCN}^-$$ and $$\hbox {CH}_2 \hbox {CN}^-$$ anions and the corresponding deuterated fragments for acetonitrile-$$\hbox {d}_3$$ by dissociative electron attachment, and measured ion yields curves of each fragment. We saw no evidence for associative electron attachment to form the parent ion in these measurements. We also have measured the kinetic energy and angular distribution of selected fragments using a velocity map imaging (VMI) spectrometer

Proton transfer from pinene stabilizes water clusters

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