|
|
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.
|
|
|
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...
|
|
|
Investigation of photodissociation dynamics implementing the velocity map imaging technique
Moriová, Kamila ; Fárník, Michal (advisor) ; Profant, Václav (referee)
The aim of this thesis is to investigate the effects of change in the chain length and chlorine group position on C-Cl bond photodissociation dynamics of chloroalkanes using the velocity map imaging (VMI) method. Three different chloroalkanes are studied (1-chloropropane, 2-chloropropane, 1-chloropentane) and compared with previously investigated chloromethane. Regardless of the parent chloroalkane, measured kinetic energy distributions (KEDs) of chlorine photofragments exhibit a single peak at energy around 0.8 eV. Photodissociation of higher chloroalkanes involves a recoil of a semi-rigid alkyl fragment, whose internal energy absorbs 40-60% of the total available energy. For chloromethane, however, only less than 10% of the available energy goes into the alkyl fragment excitation. Measured results of the energy partitioning are compared with cal- culations based on classical impulsive models. VMI experiment in combination with theory also yields information about the nature of electronic transition and probability of the intersystem crossing. Analysis indicates that the direct absorp- tion into the triplet state is more probable for the chloroalkanes with longer chain length, especially for the branched one. 1
|
|
|
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...
|
|
|
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.
|
|
|
Ion imaging method in molecular beam photodissociation experiments
Košťál, Pavel ; Fárník, Michal (advisor) ; Roučka, Štěpán (referee)
During my master thesis I became familiar with ion imaging and velocity map imaging (VMI) techniques in experiments with molecular beam. My major contribution was writing a computer program for data acquisition and pre-analysis. The program features initial filtering of the data, improving significantly signal to noise ratio. Non-trivial effort was required to make the program compatible with three different CCD cameras implemented on different experiments in the laboratory. I have also simulated ion trajectories in VMI and wrote a program code to imulate VMI image distortions due to imperfections in apparatus geometry. These programs will be useful in aligning and tuning the apparatus. Finally, I wrote a program for data manipulation and conversion to formats compatible with various data analysis programs available in the laboratory. All the above programs I have tested by measurements of 243 nm photodissociation of HBr molecules.
|
guest ::
