137 research outputs found
„Wir sprachen babylonisch kunterbunt“: literarische Kreativität bei Ilma Rakusa
No full textThis article examines the creative use of the German language in the works of Ilma Rakusa, a writer born in Slovakia and currently living in Zurich, Switzerland. In particular, the analysis deals with the collection of poems Impressum: Langsames Licht. Gedichte (2016) and the literary creativity of the author who mixes with great skill multilingual play on words, sounds, voices and alliterations, rendered through a creative manipulation of the German language. Chinese words, Hebrew names as well as entire English and French sentences can be found in Ilma Rakusa’s poems, which lead to a rhythmic, multilingual and partly rhymed texture
Dynamics of ion-molecule reactions of SO2.+with H2O and CH4
No full textThe reaction dynamics and the temperature-dependent kinetic trend of the SO2.+ion-molecule reactions with water and methane have been studied using the tunable synchrotron radiation to produce excited SO2.+ions and ab-initio methods. The experimental results show that only one product, HSO2+, is formed in both reactions and its yield displays different trends with the photon energy. DFT and VTST calculations have been used to explore the dynamics of the reactions and to calculate the rate constants at different temperatures
HSO2+ formation from ion-molecule reactions of SO2+ with water and methane: two fast reactions with reverse temperature-dependent kinetic trend
No full textIn this work an experimental and theoretical study on the formation of HSO2 + ion from the SO2 ⋅++CH4 and SO2 ⋅++H2O ion–molecule reactions at different temperatures is reported. Tunable synchrotron radiation was used to produce the SO2 ⋅+ ion in excited ro-vibrational levels of the ionic ground state X2A1 and mass spectrometry was employed to identify the product ions. Calculations in the frame of the density functional theory and variational transition state theory were combined to explore the dynamics of the reactions. The experimental results show that HSO2 + is the only product in both reactions. Its yield decreases monotonically with photon energy in the SO2 ⋅++H2O reaction, while it decreases at first and then increases in the SO2 ⋅++CH4 reaction. Theory confirms this trend by calculating the rate constants at different temperatures and explains the results by means of the polar, spin and charge effects as well as structural reorganization occurring in the reaction coordinate. The dynamic behavior observed in these two reactions is of general and fundamental interest. It can also provide some insights on the role of these reactions in astrochemistry as well as in their use as models for bond-activation reactions. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei
Photoionization mass spectrometry of ω-phenylalkylamines: Role of radical cation-π interaction
No full textLinear ω-phenylalkylamines of increasing alkyl chain length have been investigated employing synchrotron radiation in the photon energy range from 7 to 15 eV. These molecules have received considerable interest because they bear the skeleton of biologically relevant compounds including neurotransmitters and because of the possible interaction between the amino moiety and the phenyl ring. Recently, the contribution of this interaction has been assayed in both neutral and protonated species, pointing to a role of the polymethylene chain length. In this work, the ionization energy (IE) values of benzylamine (BA), 2-phenylethylamine (2-PEA), 3-phenylpropylamine (3-PPA), and 4-phenylbutylamine (4-PBA) were investigated in order to ascertain the impact of the different alkyl chain lengths and to verify an amino radical cation-π interaction. The IEs obtained experimentally, 8.54, 8.37, 8.29, and 8.31 eV for BA, 2-PEA, 3-PPA and 4-PBA, respectively, show a decreasing trend that is discussed employing calculations at the CBS-QB3 level. Moreover, the appearance energy values for major fragments produced by the photofragmentation process are reported
Photoionization of methanol: a molecular source for the prebiotic chemistry
No full textMethanol is one of the most abundant and ubiquitous molecules in the space. Its chemistry is fundamental to
understand the molecular growing from prebiotic molecules, ions and radicals. In this work the reaction of
labelled methanol CD3OH•+ radical cation, produced with different internal energies by monochromatic synchrotron
radiation, with neutral CD3OH was studied. The dynamics of the main reaction channels were investigated
by theoretical calculations. The results show how these processes can be considered suitable pathways for
the formation of fundamental species as CH3O(H)H+, CH3O•, •CH2OH, CH2O which are potential precursors to
prebiotic molecules
Excited state dynamics of Zn–salophen complexes
No full textZn–salophen complexes are a promising class of fluorescent chemosensors for nucleotides and nucleic acids. We have investigated, by means of steady state UV–Vis, ultrafast transient absorption, fluorescence emission and time dependent density functional theory (TD-DFT) the behavior of the excited states of a salicylidene tetradentate Schiff base (Sal), its Zn(II) coordination compound (Zn–Sal) and the effect of the interaction between Zn–Sal and adenosine diphosphate (ADP). TD-DFT shows that the deactivation of the excited state of Sal occurs through torsional motion, due to its rotatable bonds and twistable angles. Complexation with Zn(II) causes rigidity so that the geometry changes in the excited states with respect to the ground state structure are minimal. By addition of ADP to a freshly prepared Zn–Sal ethanol solution, a longer relaxation constant, in comparison to Zn–Sal, was measured, indicative of the interaction between Zn–Sal and ADP. After a few days, the Zn–Sal–ADP solution displayed the same static and dynamic behavior of a solution containing only the Sal ligand, demonstrating that the coordination of the ADP anion to Zn(II)leads to the demetallation of the Sal ligand. Fluorescence measurements also revealed an enhanced fluorescence at 375 nm following the addition of ADP to the solution, caused by the presence of 2,3-diamino naphthalene that is formed by demetallation and partial decomposition of the Sal ligand. The efficient fluorescence of this species at 375 nm could be selectively detected and used as a probe for the detection of ADP in solution
Ion Chemistry of Carbon Dioxide in Nonthermal Reaction with Molecular Hydrogen
No full text[Image: see text] The exothermic hydrogen transfer from H(2) to CO(2)(·)(+) leading to H and HCO(2)(+) is investigated in a combined experimental and theoretical work. The experimental mass/charge ratios of the ionic product (HCO(2)(+)) and the ionic reactant (CO(2)(·)(+)) are recorded as a function of the photoionization energy of the synchrotron radiation. Theoretical density functional calculations and variational transition state theory are employed and adapted to analyze the energetic and the kinetics of the reaction, which turns out to be barrierless and with nonthermal rate coefficients controlled by nonstatistical processes. This study aims to understand the mechanisms and energetics that drive the reactivity of the elementary reaction of CO(2)(·)(+) with H(2) in different processes
"Insights into 2-Chloropyrimidine fragmentation through a thermochemical analysis of the ionic fragments"
No full textIn the present work we have studied the photoinduced ion chemistry of the 2Cl-pyrimidine
molecule in the energy region 9−14 eV. The theoretical gas phase enthalpies of formation of the main
fragments calculated using the G3B3 and G2 ab initio methods are compared to the experimental values,
derived by the measured appearance energy of the fragments. This approach provides new insights into
both the geometric structure of the ionic fragments and the basic mechanisms governing the molecular
fragmentation
Gas Phase Oxidation of Carbon Monoxide by Sulfur Dioxide Radical Cation: Reaction Dynamics and Kinetic Trend With the Temperature
No full textGas phase ion chemistry has fundamental and applicative purposes since it allows the study of the chemical processes in a solvent free environment and represents models for reactions occurring in the space at low and high temperatures. In this work the ion-molecule reaction of sulfur dioxide ion SO2.+ with carbon monoxide CO is investigated in a joint experimental and theoretical study. The reaction is a fast and exothermic chemical oxidation of CO into more stable CO2 by a metal free species, as SO2.+, excited into ro-vibrational levels of the electronic ground state by synchrotron radiation. The results show that the reaction is hampered by the enhancement of internal energy of sulfur dioxide ion and the only ionic product is SO.+. The theoretical approach of variational transition state theory (VTST) based on density functional electronic structure calculations, shows an interesting and peculiar reaction dynamics of the interacting system along the reaction path. Two energy minima corresponding to [SO2–CO].+ and [OS–OCO].+ complexes are identified. These minima are separated by an intersystem crossing barrier which couples the bent 3B2 state of CO2 with C2v symmetry and the 1A1 state with linear D∞h symmetry. The spin and charge reorganization along the minimum energy path (MEP) are analyzed and eventually the charge and spin remain allocated to the SO.+ moiety and the stable CO2 molecule is easily produced. There is no bottleneck that slows down the reaction and the values of the rate coefficient k at different temperatures are calculated with capture theory. A value of 2.95 × 10−10 cm3s−1molecule−1 is obtained at 300 K in agreement with the literature experimental measurement of 3.00 × 10−10 ± 20% cm3s−1molecule−1, and a negative trend with temperature is predicted consistently with the experimental observations
A joint theoretical and experimental study on diiodomethane: Ions and neutrals in the gas phase
No full textThe chemical physics of halomethanes is an important and challenging topic in several areas of
chemistry in particular in the chemistry of the atmosphere. Among the class of halomethanes, the
diiodomethane molecule has attracted some interest in the last years, but despite this, the information
on its radical cation[CH2I2]·+is still limited. In this work, we measured and calculated the appearance
energy (AE) of the ionic fragments I2·+and CH2·+and correlated the different fragmentation channels
to the electronic states of the cation via photoelectron-photoion coincidence (PEPICO) experiments.In the case of the CH2/I2·+
channel, the experimentally determined AE is in excellent agreementwith the adiabatic theoretical value while a discrepancy is observed for the CH2·+/I2channel.This discrepancy can be understood accounting for a fragmentation involving the formation oftwo I atoms (CH2·+/2I channel), which, as explained by time dependent density functional theory(TD-DFT) calculations, occurs when[CH2I2]·+
excited states are involve
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