We investigate the electron attachment of acetyl chloride CH3COCl (AC) molecules and clusters in a molecular beam experiment and by extensive theoretical calculations. The main product of dissociative electron attachment (DEA) to the AC molecule is Cl-, which leads to the main (AC) n Cl- series in clusters. The weaker ion series identified in the cluster mass spectra correspond to (AC) n HCl2 - and hydrogen abstraction fragments [(AC) n -H]-, in full agreement with calculated energetics. We compare the present results for AC with previously studied trifluoroacetyl chloride CF3COCl (TFAC) and trichloroacetic acid CCl3COOH (TCA) molecules and clusters. DEA of the three isolated molecules results in the main fragment Cl-; however, the electron attachment to their clusters produces distinctly different cluster ions. This demonstrates that the outcomes of reactions of electrons with molecules in an environment cannot easily be predicted from the DEA of isolated molecules, and the solvent plays a key role in the process.

• Publikační typ
• časopisecké články MeSH

The interest in the electron impact-induced ligand release from MeCpPtMe3 [trimethyl(methylcyclopentadienyl)platinum(IV)] is motivated by its widespread use as a precursor in focused electron and ion beam nanofabrication. By experimentally studying the electron impact dissociative ionization of MeCpPtMe3 under single-collision conditions, we have found that the removal of two methyl radicals is energetically more favorable than the removal of one radical and even energetically comparable to the nondissociative ionization of MeCpPtMe3. This observation is explained by the structural rearrangement of the MeCpPtMe3+ ion prior to dissociation, resulting in the removal of ethane instead of two methyl groups. This fragmentation pathway is computationally confirmed and studied by irradiation-driven molecular dynamics (IDMD) simulations. The formation of complex molecules in irradiation-induced molecular dissociation is a general phenomenon that can occur in various molecular systems. This study explains the puzzling results of previous experiments with MeCpPtMe3 molecules and highlights the use of the IDMD approach to describe radiation-induced chemical transformations in molecular systems.

• Publikační typ
• časopisecké články MeSH

We probe the separation of ligands from iron tetracarbonyl methyl acrylate (Fe(CO)4(C4H6O2) or Fe(CO)4MA) induced by the interaction with free electrons. The motivation comes from the possible use of this molecule as a nanofabrication precursor and from the corresponding need to understand its elementary reactions fundamental to the electron-induced deposition. We utilize two complementary electron collision setups and support the interpretation of data by quantum chemical calculations. This way, both the dissociative ionization and dissociative electron attachment fragmentation channels are characterized. Considerable differences in the degree of precursor fragmentation in these two channels are observed. Interesting differences also appear when this precursor is compared to structurally similar iron pentacarbonyl. The present findings shed light on the recent electron-induced chemistry of Fe(CO)4MA on a surface under ultrahigh vacuum.

• Klíčová slova
• FEBID precursor, electron collision, focused electron beam-induced deposition (FEBID), iron tetracarbonyl methyl acrylate,
• Publikační typ
• časopisecké články MeSH

Details of electron-induced chemistry of methyl methacrylate (MMA) upon complexation are revealed by combining gas-phase 2D electron energy loss spectroscopy with electron attachment spectroscopy of isolated MMA and its clusters. We show that even though isolated MMA does not form stable parent anions, it efficiently thermalizes the incident electrons via intramolecular vibrational redistribution, leading to autodetachment of slow electrons. This autodetachment channel is reduced in clusters due to intermolecular energy transfer and stabilization of parent molecular anions. Bond breaking via dissociative electron attachment leads to an extensive range of anion products. The dominant OCH3- channel is accessible via core-excited resonances with threshold above 5 eV, despite the estimated thermodynamic threshold below 3 eV. This changes in clusters, where MnOCH3- anions are observed in a lower-lying resonance due to neutral dissociation of the 1(n, π*) state and electron self-scavenging. The present findings have implications for electron-induced chemistry in lithography with poly(methyl methacrylate).

• Publikační typ
• časopisecké články MeSH

Clusters in molecular beam experiments can mimic aerosol nanoclusters and provide molecular-level details for various processes relevant to atmospheric aerosol research. Aerosol nanoclusters, particles of sizes below 10 nm, are difficult to investigate in ambient atmosphere and thus represent a gap in our understanding of the new particle formation process. Recent field measurements and laboratory experiments are closing this gap; however, experiments with clusters in molecular beams are rarely involved. Yet, they can offer an unprecedented detailed insight into the processes including particles in this size range. In this Perspective, we discuss several up-to-date molecular beam experiments with clusters and demonstrate that the investigated clusters approach aerosol nanoclusters in terms of their complexity and chemistry. We examine remaining gaps between atmospheric aerosols and clusters in molecular beams and speculate about future experiments bridging these gaps.

• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

We investigate electron attachment to large ammonia clusters doped with a single benzene (Bz) molecule (NH3)N·Bz, N̄ ≈ 320. Negatively charged clusters are probed by mass spectrometry, and the energy-dependent ion yields are derived from mass spectra measured at different electron energies. The ion efficiency curves of pure ammonia clusters exhibit two maxima. At around 6 eV, (NH3)n-1NH2- ions are produced via dissociative electron attachment (DEA) to NH3 molecules. (NH3)n- ions produced at this energy are formed by DEA followed by fragment caging. At low energies around 1.3 eV, only (NH3)n- ions are formed for cluster sizes n ≥ 35 that correspond to solvated electrons in ammonia clusters. The doped (NH3)n·Bz- cluster ions exhibit essentially the same energy dependence. The (NH3)n·Bz- ions are metastable and evaporate NH3 molecule(s), while pure (NH3)n- ions are stable. The lifetime for NH3 molecule evaporation from the Bz-doped clusters was estimated as τ ≈ 18 μs. We interpret the metastability of the doped clusters by the charge localization on a Bz- ion solvated in the ammonia, which is accompanied by an energy release leading to the evaporation of NH3 molecule(s).

• Publikační typ
• časopisecké články MeSH

The uptake of molecules on nanometer-size clusters of polyaromatic hydrocarbons (PAHs) is important for the condensation of water on PAH aerosols in the atmosphere and for ice mantle growth on nanoparticles in the interstellar medium. We generate benzene clusters BzN of mean size N̅ ≈ 300 (radius R̅ ≈ 2.2 Å) as a model system for the PAH nanoparticles. Using molecular beams and mass spectrometry detection, we investigate the uptake of water, methanol, and ethanol by these clusters. All picked up molecules are highly mobile on BzN and generate clusters within <3 ms. The relative uptakes for the different investigated molecules can be directly compared and quantified. Water molecules exhibit the lowest relative pickup probability that is ∼30% lower than those for methanol and ethanol, which are approximately the same.

• Publikační typ
• časopisecké články MeSH

The dominant pathway of radiation damage begins with the ionization of water. Thus far, however, the underlying primary processes could not be conclusively elucidated. Here, we directly study the earliest steps of extreme ultraviolet (XUV)-induced water radiolysis through one-photon excitation of large water clusters using time-resolved photoelectron imaging. Results are presented for H2O and D2O clusters using femtosecond pump pulses centered at 133 or 80 nm. In both excitation schemes, hydrogen or proton transfer is observed to yield a prehydrated electron within 30 to 60 fs, followed by its solvation in 0.3 to 1.0 ps and its decay through geminate recombination on a ∼10-ps time scale. These results are interpreted by comparison with detailed multiconfigurational non-adiabatic ab-initio molecular dynamics calculations. Our results provide the first comprehensive picture of the primary steps of radiation chemistry and radiation damage and demonstrate new approaches for their study with unprecedented time resolution.

• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

We study the reactivity of misonidazole with low-energy electrons in a water environment combining experiment and theoretical modelling. The environment is modelled by sequential hydration of misonidazole clusters in vacuum. The well-defined experimental conditions enable computational modeling of the observed reactions. While the NO 2 - dissociative electron attachment channel is suppressed, as also observed previously for other molecules, the OH - channel remains open. Such behavior is enabled by the high hydration energy of OH - and ring formation in the neutral radical co-fragment. These observations help to understand the mechanism of bio-reductive drug action. Electron-induced formation of covalent bonds is then important not only for biological processes but may find applications also in technology.

• Klíčová slova
• bond formation, clusters, electron attachment, low-energy electron, misonidazole,
• MeSH
• elektrony * MeSH
• misonidazol chemie   MeSH
• molekulární modely MeSH
• molekulární struktura MeSH
• rozpouštědla MeSH
• spektrální analýza MeSH
• teoretické modely MeSH
• voda MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• misonidazol MeSH
• rozpouštědla MeSH
• voda MeSH