Fotodisociace molekul ve volných nanočásticích

Several experiments with various clusters were performed on a molecular beam apparatus. (1) The beam velocities were measured for rare gases and water clusters under various expansion conditions to learn about the supersonic expansions and cluster generation processes. (2) The photodissociation of (HBr)n clusters was measured for calibration purposes. (3) The mass spectrometry of clusters of small biomolecules imidazole, pyrazole and pyrrole was investigated. The stabilization of these hydrogen bonded species in the excited states by hydrogen transfer process was revealed, relevant to the stability of biomolecules in general. (4) Finally, the photodissociation of an HI molecule on water clusters (H2O)n was studied and compared to the photodissociation on (Ar)n clusters. It was shown that HI molecules acidically dissociate on (H2O)n and generate zwitterionic species H3O+ I-(H2O)n-1, which are then excited into biradical states with the neutral hydronium molecule H3O.Na aparatuře s molekulovými paprsky bylo provedeno několik experimentů s různými klastry. (1) Byly změřeny rychlosti klastrů vzácných plynů a vody za různých expanzních podmínek, abychom se učili o supersonické expanzi a procesech tvorby klastrů. (2) Fotodisociace klastrů (HBr)n byla změřena kvůli kalibraci. (3) Hmotová spektroskopie klastrů malých biomolekul imidazolu, pyrazolu a pyrolu byla zkoumána. Byla odhalena stabilizace těchto molekul, které jsou vázany vodíkovými vazbami, přenosem vodíku, což je relevantní ke stabilitě biomolekul obecně. (4) Konečně, fotodisociace molekuly HI na klastrech vody (H2O)n byla studována a porovnána s fotodisociací na klastrech argonu (Ar)n. Bylo ukázáno, že molekula HI podléhá acidické disociaci na (H2O)n za tvorby obojetného ionu H3O+ I-(H2O)n-1, který je následně excitován do biradikálového stavu s neutrální molekulou H3O.Department of Chemical Physics and OpticsKatedra chemické fyziky a optikyFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Rydberg states of helium in electric and magnetic fields of arbitrary relative orientation

A spectroscopic study of Rydberg states of helium ($n$ = 30 and 45) in magnetic, electric and combined magnetic and electric fields with arbitrary relative orientations of the field vectors is presented. The emphasis is on two special cases where (i) the diamagnetic term is negligible and both paramagnetic Zeeman and Stark effects are linear ($n$ = 30, $B \leq$ 120 mT and $F$ = 0 - 78 V/cm ), and (ii) the diamagnetic term is dominant and the Stark effect is linear ($n$ = 45, $B$ = 277 mT and $F$ = 0 - 8 V/cm). Both cases correspond to regimes where the interactions induced by the electric and magnetic fields are much weaker than the Coulomb interaction, but much stronger than the spin-orbit interaction. The experimental spectra are compared to spectra calculated by determining the eigenvalues of the Hamiltonian matrix describing helium Rydberg states in the external fields. The spectra and the calculated energy-level diagrams in external fields reveal avoided crossings between levels of different $m_l$ values and pronounced $m_l$-mixing effects at all angles between the electric and magnetic field vectors other than 0. These observations are discussed in the context of the development of a method to generate dense samples of cold atoms and molecules in a magnetic trap following Rydberg-Stark deceleration.Comment: 16 pages, 18 figure

Influence of domain walls thickness, density and alignment on Barkhausen noise emission in low alloyed steels

This study deals with the characterization of low alloyed steels of diferent yield strengths (varying in the range of 235–1100 MPa) via Barkhausen noise emission. The study investigates the potential of this technique to distinguish among the low alloyed steels and all signifcant aspects contributing to Barkhausen noise, such as the residual stress state, microstructure expressed in terms of dislocation density, grain size, prevailing phase, as well as associated aspects of the domain wall substructure (domain wall thickness, energy, their spacing and density in the matrix). Barkhausen noise in the rolling as well as transversal direction grows along with the yield strength (up to 500 MPa) and the corresponding grain refnement of ferrite. As soon as the martensite transformation occurs in a high strength matrix, this evolution saturates, and remarkable magnetic anisotropy is developed when Barkhausen noise in the transversal direction grows at the expense of the rolling direction. The contribution of residual stresses as well as the domain wall thickness is only minor, and the evolution of Barkhausen noise is driven by the density of the domain walls and their realignment.Web of Science131art. no. 568

Collision dynamics of symmetric top molecules:A comparison of the rotationally inelastic scattering of CD3 and ND3 with He

Contains fulltext : 133180.pdf (publisher's version ) (Open Access

Rotationally inelastic scattering of ND 3

Differential cross sections (DCSs) are reported for rotationally inelastic scattering of ND3 with H2, measured using a crossed molecular beam apparatus with velocity map imaging (VMI). ND3 molecules were quantum-state selected in the ground electronic and vibrational levels and, optionally, in the j±k = 14- rotation-inversion level prior to collisions. Inelastic scattering of state-selected ND3 with H2 was measured at the mean collision energy of 580 cm-1 by resonance-enhanced multiphoton ionisation spectroscopy and VMI of ND3 in selected single final j'±k' levels. Comparison of experimental DCSs with close-coupling quantum-mechanical scattering calculations serves as a test of a recently reported ab initio potential energy surface. Calculated integral cross sections reveal the propensities for scattering into various final j'±k' levels of ND3 and differences between scattering by ortho and para H2. Integral and differential cross sections are also computed at a mean collision energy of 430 cm-1 and compared to our recent results for inelastic scattering of state-selected ND3 with He.</p

Study of proper and improper microwave dielectric losses by means of teraherz and infrared spectroscopy

Title: Study ol"proper and improper microwave dielectric tosses by means of tcrahcrz and infrared speetroseopy Author: Ondfej Tkac Department: Department of Dielectrics. Institute of Physics, Academy of Sciences of C/ech Republic Supervisor: RNDr. Slanislav Kamba.C'Sc.. Na Slovance 2. Prague 8 Supervisor's e-mail adress: kambawT/u.c/ Abstract: In the llrst part of this thesis there is described relevant theory, especially we pay our attention to the principles of infrared speetroseopy and fitting models, then to the explanation of the terms proper and improper dielectric losses and we also discuss dielectrics and ferroelectrics. By means of Fourier transform infrared speetroseopy we measured infrared spectra at room temperature in the range of 30 - 3000 em"1. We lilted the spectra and then we extrapolated the final complex permit!vity into the microwave range. This enabled us to estimate the proportion of improper dielectric losses on total microwave losses. By the ceramic SiVxPlxCeVfinO-^ (.\0 to 9) we studied the impact of amount of lead on dielectric properties. We found out that the substitution of strontium with lead causes the increase of permitivity up lo several thousands and forces ferroelectric transition for x>2. With perovskitc Ca/n, jNb^ :,-xVx(.)1 (.v=0 to 0,01) we examined the inlluence of..