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Photodissociation of small polyatomic molecules investigated via molecular beam and velocity map imaging techniques
Vinklárek, Ivo ; Fárník, Michal (advisor) ; Wester, Roland (referee) ; Klán, Petr (referee)
Velocity map imaging (VMI) combined with supersonically expanded molecules pro- vides molecular-level insight into many fundamental natural phenomena. This compre- hensive work delivers an introduction to the photodissociation theory and applied VMI and mass spectrometric experimental techniques, followed by an overview of our achieve- ments in the investigation of photodissociation and clustering on the selected molecular systems. Also, new implementations of the centroiding mode and the current status of the apparatus for imaging are commented on for future measurements. The first part of the experimental results focuses on fundamental research of photodissociation of isolated molecules. We demonstrate an efficient coupling between the stretching vibration and ejection of hydrogen radical in pyrrole and, furthermore, describe the impact of singlet- triplet dynamics and molecular frame on energy redistribution during the fragmentation of selected chloroalkanes. The second part revolves around chloroalkane clusters in the perspective of atmospheric chemistry, which is represented by the observations of differ- ent dynamics for CH3 and Cl fragments in (CH3Cl)n cluster photodissociation. Finally, the clustering research is extended by our recent pickup experiments with clusters of polyaromatic hydrocarbons...
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Modelling of precursors for electron-beam induced deposition
Andreides, Benjamín ; Fedor, Juraj (advisor) ; Fárník, Michal (referee)
1 Abstract FEBID (focused electron beam induced deposition) precursors are a subject of active research both in experimental and computer simulation manners. Their potential use in FEBID is strongly dependent on the completeness of the disso- ciation process caused by both primary and secondary electrons of the electron beam. This work focuses on exploration of dissociation process of iron pentacar- bonyl cation by secondary electrons in i) vacuum ii) argon cluster environment and on possibility of utilizing argon cluster with an embedded gold particle as a non-covalently bonded precursor for FEBID. These systems will be inspected via means of the classical and reactive molecular dynamics using the rCHARMM force field. 1
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Monte-Carlo simulation of photodissociation spectra from molecular beam experiment
Košťál, Pavel ; Fárník, Michal (advisor) ; Havlíček, Josef (referee)
Within the framework of my BSc Thesis I became familiar with a unique molecular beam apparatus for cluster studies. I have learned about clusters and molecular beams, mass spectrometry, photodissociation and molecular dynamics. My specific task was to generace several computer programs for data acquisition and evaluation of~the~present experiments: (1) A program for TOF to mass spectra conversion. This program facilitated immediate evaluation of~the~measured mass spectra. (2) A program for TOF spectra conversion into the kinetic energy distribution KED of the fragments, which provides immediate information about the studied photochemical processes. The immediate information provided by both these programs enable a more effective control of the experiment. (3) Finally, I have modified Monte-Carlo simulation program. This program serves the ultimate TOF→ KED conversion of the experimental data. All the programs were tested with photodissociation of a well studied system of HBr cluster, and they have shown a good performance.
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Mass spectrometric and optical spectroscopy studies of clusters and nanoparticles in molecular beams
Moriová, Kamila ; Fárník, Michal (advisor) ; Kopecký, Vladimír (referee)
Title: Mass spectrometric and optical spectroscopy studies of clusters and nano- particles in molecular beams Author: Kamila Moriová Institue: Institute of Physics of Charles University Supervisor: doc. Mgr. Michal Fárník, Ph.D., DSc., J. Heyrovský Institute of Phy- sical Chemistry of the CAS Consultant: RNDr. Václav Profant, Ph.D., Institute of Physics of Charles Uni- versity Abstract: Condensation of ices on the surface of dust grains with activation of these ices by cosmic rays in interstellar medium can lead to formation of complex chemical species. In the present work we primarily examine ammonia clusters, which represent a model system of ice particles. Large ammonia clusters were prepared in molecular beams and pass through a pickup chamber in which me- thanol molecules were captured. After electron ionization of (NH3)N (CH3OH)M clusters, a mass spectrum of ionic fragments was obtained in which fragments with methanol (NH3)n(CH3OH)mH+ predominated over the pure ammonia frag- ments (NH3)nH+ : at least one methanol molecule was present in 75 % fragments. This is in disproportion with the composition of the original neutral precursors, which contain less than 4 % of methanol. Based on the measurement results, we suggest that ammonia is ionized in the first place resulting in the NH+ 4 ion core solvated...
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Implementation of ion imaging technique in experiments with free molecules, clusters and nanoparticles
Kočišek, Jaroslav ; Fárník, Michal (advisor) ; Klán, Petr (referee) ; Glosík, Juraj (referee)
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, nanoparticles
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Recombination of ions in plasma at 50-300 K
Rubovič, Peter ; Glosík, Juraj (advisor) ; Fárník, Michal (referee) ; Korolov, Ihor (referee)
A B S T R A C T Title: Recombination of Ions in Plasma at 50 − 300 K Author: Peter Rubovič Supervisor: Prof. RNDr. Juraj Glosík, DrSc. Abstract: Main part of this doctoral thesis lies in a study of recom- bination of atomic and molecular ions in low temperature plasmatic environment with emphasis on effect of third bodies. Stationary After- glow equipped with Cavity Ring Down Spectrometer and Cryogenic Flowing Afterglow with Langmuir Probe II were used to obtain recom- bination rate coefficients. Electron assisted collisional radiative recom- bination of Ar+ ion was studied in the temperature range of 50−100 K and helium assisted collisional radiative recombination was observed too. Both H+ 3 and its isotopologue D+ 3 were studies in flowing after- glow and spectroscopically in stationary afterglow as well. Binary re- combination rate coefficients and ternary recombination rate coeffi- cients for helium assisted ternary recombination were determined in the temperature range of 50 − 250 K. These coefficients were deter- mined also for pure ortho- and para- nuclear spin configurations of H+ 3 in the temperature range of 80 − 200 K. Keywords: dissociative recombination, collisional radiative recombi- nation, H+ 3 , D+ 3 , Ar+ viii
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