Imaging photoelectron photoion coincidence spectroscopy with velocity focusing electron optics

An imaging photoelectron photoion coincidence spectrometer at the vacuum ultraviolet (VUV) beamline of the Swiss Light Source is presented and a few initial measurements are reported. Monochromatic synchrotron VUV radiation ionizes the cooled or thermal gas-phase sample. Photoelectrons are velocity focused, with better than 1 meV resolution for threshold electrons, and also act as start signal for the ion time-of-flight analysis. The ions are accelerated in a relatively low, 40-80 V cm(-1) field, which enables the direct measurement of rate constants in the 10(3)-10(7) s(-1) range. All electron and ion events are recorded in a triggerless multiple-start/multiple-stop setup, which makes it possible to carry out coincidence experiments at >100 kHz event frequencies. As examples, the threshold photoelectron spectrum of the argon dimer and the breakdown diagrams for hydrogen atom loss in room temperature methane and the chlorine atom loss in cold chlorobenzene are shown and discussed

Spectroscopy of Isolated Prebiotic Nucleobases

We use multiphoton ionization and double resonance spectroscopy to study the excited state dynamics of biologically relevant molecules as well as prebiotic nucleobases, isolated in the gas phase. Molecules that are biologically relevant to life today tend to exhibit short excited state lifetimes compared to similar but non-biologically relevant analogs. The mechanism is internal conversion, which may help protect the biologically active molecules from UV damage. This process is governed by conical intersections that depend very strongly on molecular structure. Therefore we have studied purines and pyrimidines with systematic variations of structure, including substitutions, tautomeric forms, and cluster structures that represent different base pair binding motifs. These structural variations also include possible alternate base pairs that may shed light on prebiotic chemistry. With this in mind we have begun to probe the ultrafast dynamics of molecules that exhibit very short excited states and search for evidence of internal conversions

Interplay among electrostatic, dispersion and steric interactions: Spectroscopy and quantum chemical calculations of π-hydrogen bonded complexes

π-hydrogen bonding interactions are ubiquitous in both materials and biology. Despite their relatively weak nature great progress has been made in their investigation by experimental and theoretical methods, but this becomes significantly more complicated when secondary intermolecular interactions are present. In this study the effect of successive methyl substitution on the supramolecular structure and interaction energy of indole⋯methylated benzene (ind⋯n-mb, n = 1–6) complexes is probed through a combination of supersonic jet experiment and benchmark quality quantum chemical calculations. It is demonstrated that additional secondary interactions introduce a subtle interplay among electrostatic and dispersion forces, as well as steric repulsion, which fine-tunes the overall structural motif. Resonant Two-Photon Ionization (R2PI) and IR-UV double resonance spectroscopy techniques were used to probe jet-cooled ind⋯n-mb (n = 2, 3, 6) complexes, with red-shifting of the N–H IR stretching frequency showing that increasing the degree of methyl substitution increases the strength of the primary N–H⋯π interaction. Ab initio harmonic frequency and binding energy calculations confirm this trend for all six complexes. Electronic spectra of the three dimers are broad and structureless, with quantum chemical calculations revealing that this is likely due to multiple tilted conformations of each dimer possessing similar stabilization energies

Színházak drámapedagógiai programjai által teremtett közösségek hatása a fiatalokra

Szakdolgozatomban a közösségek egyénre gyakorolt hatásán, valamint a drámapedagógia módszerének előnyein túl kérdőíves kutatással, valamint szakemberekkel készített interjúkkal vizsgálom a drámapedagógia módszere által a fiatalok személyiségfejlődési lehetőségeit. Kutatom továbbá az ifjúság színházlátogatási szokásait, színházak által biztosított programokkal kapcsolatos igényeit, ezeken történő részvételt befolyásoló tényezőket, valamint tapasztalataikat az általuk meglátogatott programokról

Structure of 2,4-Diaminopyrimidine-Theobromine Alternate Base Pairs

We report the structure of dusters of 2,4-diaminopyrimidine with 3,7-dimethylxanthine (theobromine) in the gas phase determined by IR-UV double resonance spectroscopy in both the near-IR and mid-IR regions in combination with ab initio computations. These clusters represent potential alternate nucleobase pairs, geometrically equivalent to guanine cytosine. We have found the four lowest energy structures, which include the Watson Crick base pairing motif. This Watson Crick structure has not been observed by resonant two-photon ionization (R2PI) in the gas phase for the canonical DNA base pairs

Effect of substituents on the excited-state dynamics of the modified DNA bases 2,4-diaminopyrimidine and 2,6-diaminopurine

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