Recombination of molecular ions with electrons at low temperatures

Předmětem práce je experimentální studium rekombinace molekulárních iontů s elektrony v dohasínajícím plazmatu při nízkých teplotách (< 300 K). Jsou zde popsány základy používaných diagnostických metod a modelování chemické kine- tiky, aparatury Cryo-FALP II a SA-CRDS používané v provedených experimen- tech. V rámci práce byly studovány dva procesy rekombinace iontů H+ 3 s elektrony: binární disociativní rekombinace stavů para-H+ 3 a ortho-H+ 3 a ternární vodíkem asistovaná rekombinace. Hlavním výsledkem studia binární disociativní rekombi- nace iontů H+ 3 je, že rychlost rekombinace stavu para-H+ 3 je alespoň třikrát větší než stavu ortho-H+ 3 při teplotě 60 K. Studium vodíkem asistované rekombinace poskytlo podrobnější představu o ternárních procesech rekombinace iontů H+ 3 a vyjasnilo další rozdíly mezi výsledky plazmatických experimentů.The aim of this work is the experimental study of recombination of molecular ions with electrons at low temperatures (< 300 K). The work gives an overview of the diagnostic methods, modelling of chemical kinetics, and experimental ap- paratuses Cryo-FALP II and SA-CRDS used in the undertaken measurements. Two processes were studied in the course of this work: state-selective binary disso- ciative recombination of H+ 3 ions in para-H+ 3 and ortho-H+ 3 states, and H2-assisted ternary recombination of H+ 3 . The main result of the state-selective dissociative recombination study is that the rate of recombination in the para-H+ 3 state is at least three times higher than in the ortho-H+ 3 state at 60 K. The study of H2- assisted recombination gave a better understanding of ternary processes of H+ 3 ions and removed further discrepancies between results of afterglow experiments.Department of Surface and Plasma ScienceKatedra fyziky povrchů a plazmatuFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Experimental Determination of the Dissociative Recombination Rate Coefficient for Rotationally Cold CH⁺ and Its Implications for Diffuse Cloud Chemistry

Observations of CH+ are used to trace the physical properties of diffuse clouds, but this requires an accurate understanding of the underlying CH+ chemistry. Until this work, the most uncertain reaction in that chemistry was dissociative recombination (DR) of CH+. Using an electron–ion merged-beams experiment at the Cryogenic Storage Ring, we have determined the DR rate coefficient of the CH+ electronic, vibrational, and rotational ground state applicable for different diffuse cloud conditions. Our results reduce the previously unrecognized order-of-magnitude uncertainty in the CH+ DR rate coefficient to ∼20% and are applicable at all temperatures relevant to diffuse clouds, ranging from quiescent gas to gas locally heated by processes such as shocks and turbulence. Based on a simple chemical network, we find that DR can be an important destruction mechanism at temperatures relevant to quiescent gas. As the temperature increases locally, DR can continue to be important up to temperatures of ∼600 K, if there is also a corresponding increase in the electron fraction of the gas. Our new CH+ DR rate-coefficient data will increase the reliability of future studies of diffuse cloud physical properties via CH+ abundance observations

Laser-probing the rotational cooling of molecular ions by electron collisions

We present state-selected measurements of rotational cooling and excitation rates of CH$^+$ molecular ions by inelastic electron collisions. The experiments are carried out at the Cryogenic Storage Ring, making use of a monoenergetic electron beam at matched velocity in combination with state-sensitive laser-dissociation of the CH$^+$ ions for simultaneous monitoring of the rotational level populations. Employing storage times of up to 600 s, we create conditions where electron-induced cooling to the $J = 0$ ground state dominates over radiative relaxation, allowing for the experimental determination of inelastic electron collision rates to benchmark state-of-the-art theoretical calculations. On a broader scale, our experiments pave the way to probe inelastic electron collisions for a variety of molecular ions relevant in various plasma environments.Comment: Main paper: PDFLaTeX with 7 pages, 4 figures. Supplemental material: PDFLaTeX with 26 pages, 11 figures, 5 tables. This article has been accepted by Physical Review Letter

Direct and inverse opal photonic crystals: theoretical analysis and experimental realization

katedra fyzikální elektronik

Penalizační metody ve stochastické optimalizaci

The submitted thesis studies penalty function methods for stochastic programming problems. The main objective of the paper is to examine penalty function methods for deterministic nonlinear programming, in particular exact penalty function methods, in order to enhance penalty function methods for stochastic programming. For this purpose, the equivalence of the original de- terministic nonlinear and the corresponding penalty function problem using arbi- trary vector norm as the penalty function is shown for convex and invex functions occurring in the problems, respectively. The obtained theorems are consequently applied to multiple chance constrained problems under finite discrete probability distribution to show the asymptotic equivalence of the probabilistic and the cor- responding penalty function problems. The practical use of the newly obtained methods is demonstrated on a numerical study, in which a comparison with other approaches is provided as well.

Elementary Processes at Low Temperatures - Reactions of H3+ and N2H+ in Afterglow Plasmas

Electron-ion recombination and ion-neutral interactions play a piv- otal role in the chemical evolution of molecules in the Interstellar Medium (ISM). Physical conditions under which these processes un- dergo in the ISM include a wide range of temperatures and particle number densities. This work contributes to the experimental study of named low temperature phenomena in the range of 30 K to 300 K focusing on the reactions of hydrogen-containing light molecules. The employed experimental techniques are based on a combination of a Stationary Afterglow (SA) instrument with a Continuous Wave Cavity Ring-down Spectrometer (cw-CRDS). The main contributions of this work can be split into three topics. (1) The proton and deuteron con- taining isotopic system of H3 + ions. The isotopic fractionation process in collisions with hydrogen and deuterium gas was investigated in low temperature discharges, nominal ion temperatures of 80 K to 140 K, to deduce relative ion densities in the experiments. These are necessary for afterglow studies of isotopic effects in electron-ion recombination of the studied ions. (2) Vibrational spectroscopy of N2H+ ions focusing on first overtone (2ν1 band) transitions and ion thermometry, the first step towards studies of electron-ion recombination. (3) The role of para/ortho spin..

Elementární procesy p̌ri nízkých teplotách - reakce iont ̊u H3+ a N2H+ v dohasínajícím plazmatu

Elektron-iontová rekombinace a iont-neutrální interakce hrají klí- ̌covou roli v chemickém vývoji molekul v mezihv̌ezdném prostoru. Podmínky v mezihv̌ezdném prostoru p̌ri kterých tyto procesy probí- hají zahrnují široký rozsah teplot a hustot ̌cástic. Tato práce je zam̌e- ̌rena na experimentální studium uvedených nízkoteplotních proces̊u v teplotním rozsahu od 30 K do 300 K, zejména na reakce malých molekul obsahujících vodíkové atomy. Použitá experimentální tech- nika je založena na kombinaci prosťredí dohasínajícího plazmatu se Continuous Wave Cavity Ring-down spektrometrem. Mezi ťri hlavní výstupy práce paťrí: Za prvé: studium izotopického systému iont̊u H3 + obsahující protony a deuterony. Pr̊ub̌eh izotopické frakcionace ve srážkách s vodíkem a deuteriem byl studován v nízkoteplotních výbojích, v nominálním rozsahu teplot od 80 K do 140 K. V experimen- tech byly odvozeny relativní koncentrace iont̊u, nezbytné pro studium izotopických efekt̊u v elektron-iontové rekombinaci v dohasínajícím plazmatu studovaných iont̊u. Za druhé: vibrǎcní spektroskopie iont̊u N2H+ zam̌ěrená na takzvané "first overtone" (2ν1 pás) p̌rechody a termometrie využitím iont̊u. Experimenty p̌redstavují první krok k studiu elektron-iontové rekombinace vybraného iontu. Za ťretí: stu- dium role para/ortho spinových stav̊u v...Electron-ion recombination and ion-neutral interactions play a piv- otal role in the chemical evolution of molecules in the Interstellar Medium (ISM). Physical conditions under which these processes un- dergo in the ISM include a wide range of temperatures and particle number densities. This work contributes to the experimental study of named low temperature phenomena in the range of 30 K to 300 K focusing on the reactions of hydrogen-containing light molecules. The employed experimental techniques are based on a combination of a Stationary Afterglow (SA) instrument with a Continuous Wave Cavity Ring-down Spectrometer (cw-CRDS). The main contributions of this work can be split into three topics. (1) The proton and deuteron con- taining isotopic system of H3 + ions. The isotopic fractionation process in collisions with hydrogen and deuterium gas was investigated in low temperature discharges, nominal ion temperatures of 80 K to 140 K, to deduce relative ion densities in the experiments. These are necessary for afterglow studies of isotopic effects in electron-ion recombination of the studied ions. (2) Vibrational spectroscopy of N2H+ ions focusing on first overtone (2ν1 band) transitions and ion thermometry, the first step towards studies of electron-ion recombination. (3) The role of para/ortho spin...Katedra fyziky povrchů a plazmatuDepartment of Surface and Plasma ScienceMatematicko-fyzikální fakultaFaculty of Mathematics and Physic

The Kelly Criterion

The present work is devoted to the Kelly criterion, which is a simple method for choosing the amount of the bet for gambles with a positive expected value. In the first part of the work we introduce the mathematical explanation of the criterion, examine the capital after $n$ trials as a function of the bet, the long-run rate of return and asymptotical properties of the capital growth. In the second part we attempt to generalize the Kelly criterion from the first part for some other situations. Examples for a simple game and generalized situations illustrating the properties of the Kelly criterion and results from previous parts compose the last part of the work

Elementary Processes at Low Temperatures - Reactions of H3+ and N2H+ in Afterglow Plasmas

Electron-ion recombination and ion-neutral interactions play a piv- otal role in the chemical evolution of molecules in the Interstellar Medium (ISM). Physical conditions under which these processes un- dergo in the ISM include a wide range of temperatures and particle number densities. This work contributes to the experimental study of named low temperature phenomena in the range of 30 K to 300 K focusing on the reactions of hydrogen-containing light molecules. The employed experimental techniques are based on a combination of a Stationary Afterglow (SA) instrument with a Continuous Wave Cavity Ring-down Spectrometer (cw-CRDS). The main contributions of this work can be split into three topics. (1) The proton and deuteron con- taining isotopic system of H3 + ions. The isotopic fractionation process in collisions with hydrogen and deuterium gas was investigated in low temperature discharges, nominal ion temperatures of 80 K to 140 K, to deduce relative ion densities in the experiments. These are necessary for afterglow studies of isotopic effects in electron-ion recombination of the studied ions. (2) Vibrational spectroscopy of N2H+ ions focusing on first overtone (2ν1 band) transitions and ion thermometry, the first step towards studies of electron-ion recombination. (3) The role of para/ortho spin..

Study of reactions of simple ions in low temperature plasma

The subject of this thesis is the study of the probe diagnostic method of low temperature plasma. The basis of Langmuir probe diagnostics in terms of appli- cation on apparatus CryoFALP II for the study of reactions of simply particles, the principle of the FALP technique and the experimental method of undertaken measurements are described. As a part of the thesis a package of evaluation pro- grams were compiled, which are ready to be a part of the measuring system as described in the thesis. Main results concern verification of the proper application of Langmuir probe technique in conditions characteristic for the apparatus, argon plasma was chosen as the medium of the measurements, where the characteristic loss process is ambipolar diffusion of charged particles. The application of the acquired knowledge is shown on recombination in oxygen plasma