Does HNO dissociate on gas-phase ice nanoparticles?

We investigated the dissociation of nitric acid on large water clusters (HO), ≈ 30-500, , ice nanoparticles with diameters of 1-3 nm, in a molecular beam. The (HO) clusters were doped with single HNO molecules in a pickup cell and probed by mass spectrometry after a low-energy (1.5-15 eV) electron attachment.

Gas phase CH anion: Electronic stabilization by opening of the benzene ring.

It is well established that an isolated benzene radical anion is not electronically stable. In the present study, we experimentally show that electron attachment to benzene clusters leads to weak albeit unequivocal occurrence of a CH moiety. We propose here-based on electronic structure calculation-that this moiety actually corresponds to linear structures formed by the opening of the benzene ring via electron attachment.

Stabilization of benzene radical anion in ammonia clusters.

We investigate electron attachment to large ammonia clusters doped with a single benzene (Bz) molecule (NH)·Bz, ≈ 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.

Low-Energy Electron Induced Reactions in Metronidazole at Different Solvation Conditions.

Metronidazole belongs to the class of nitroimidazole molecules and has been considered as a potential radiosensitizer for radiation therapy. During the irradiation of biological tissue, secondary electrons are released that may interact with molecules of the surrounding environment. Here, we present a study of electron attachment to metronidazole that aims to investigate possible reactions in the molecule upon anion formation.

Uptake of Hydrogen Bonding Molecules by Benzene Nanoparticles.

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 Bz of mean size ≈ 300 (radius ≈ 2.2 Å) as a model system for the PAH nanoparticles.

Effect of Hydration on Electron Attachment to Methanesulfonic Acid Clusters.

We report an experimental and computational study of the electron-induced chemistry of methanesulfonic acid (MSA, MeSOH) in clusters. We combine the mass spectra after the 70 eV electron ionization with the negative ion spectra after electron attachment (EA) at low electron energies of 0-15 eV of the MSA molecule, small MSA clusters, and microhydrated MSA clusters to reveal the solvation effects. The MSA/He coexpansion only generates small MSA clusters with up to four molecules, but adding water substantially hydrates the MSA clusters, resulting in clusters composed of 1-2 MSA molecules accompanied by quite a few water molecules.

Bimolecular reactions on sticky and slippery clusters: Electron-induced reactions of hydrogen peroxide.

Nanoparticles can serve as an efficient reaction environment for bimolecular reactions as the reactants concentrate either inside the nanoparticle or on the surface of the nanoparticle. The reaction rate is then controlled by the rate of formation of the reaction pairs. We demonstrate this concept on the example of electron-induced reactions in hydrogen peroxide.

Heterogeneous Reactions of Methane with Cl Radicals on Large Ar Clusters.

Heterogeneous chemistry on the surfaces of atmospheric particles has a wide impact on the properties and composition of the Earth's atmosphere. In laboratory studies, clusters can represent proxies to atmospheric aerosols and help to discern the individual steps in reactions on or in aerosols. We investigate the reactivity of Cl and CCl radicals with methane on argon clusters using the pickup method.

Water-Assisted Electron-Induced Chemistry of the Nanofabrication Precursor Iron Pentacarbonyl.

Focused electron beam deposition often requires the use of purification techniques to increase the metal content of the respective deposit. One of the promising methods is adding HO vapor as a reactive agent during the electron irradiation. However, various contrary effects of such addition have been reported depending on the experimental condition.

Stability of pyruvic acid clusters upon slow electron attachment.

Pyruvic acid represents a key molecule in prebiotic chemistry and it has recently been proposed to be synthesized on interstellar ices. In order to probe the stability of pyruvic acid in the interstellar medium with respect to decomposition by slow electrons, we investigate the electron attachment to its homomolecular and heteromolecular clusters. Using mass spectrometry, we follow the changes in the fragmentation pattern and its dependence on the electron energy for various cluster sizes of pure and microhydrated pyruvic acid.

Pickup and reactions of molecules on clusters relevant for atmospheric and interstellar processes.

In this perspective, we review experiments with molecules picked up on large clusters in molecular beams with the focus on the processes in atmospheric and interstellar chemistry. First, we concentrate on the pickup itself, and we discuss the pickup cross sections. We measure the uptake of different atmospheric molecules on mixed nitric acid-water clusters and determine the accommodation coefficients relevant for aerosol formation in the Earth's atmosphere.

Ion and radical chemistry in (HO) clusters.

We investigate the ionization induced chemistry of hydrogen peroxide in (HO) clusters generated after the pickup of individual HO molecules on large free Ar, M[combining macron]≈ 160, nanoparticles in molecular beams. Positive and negative ion mass spectra are recorded after an electron ionization of the clusters at energies 5-70 eV and after a slow electron attachment (below 4 eV), respectively. The spectra demonstrate that (HO) clusters with N≥ 20 are formed on argon nanoparticles.

Photochemistry of Amylene Double Bond in Clusters on Free Argon Nanoparticles.

We have investigated reactivity of double bond in 2-methyl-2-butene (also trimethylethylene or amylene) in the excited and ionized states. In a combined experimental and theoretical study, we focused on both the intermolecular and intramolecular reactions. In a molecular beam experiment, we have sequentially picked up several amylene molecules on the surface of argon nanoparticles Ar, ≈ 90, acting as a cold support.

Oxidation Enhances Aerosol Nucleation: Measurement of Kinetic Pickup Probability of Organic Molecules on Hydrated Acid Clusters.

We investigate the uptake of the most prominent biogenic volatile organic compounds (VOCs)-isoprene, α-pinene, and their selected oxidation products-by hydrated acid clusters in a molecular beam experiment and by DFT calculations. Our experiments provide a unique and direct way of determination of the surface accommodation coefficient () on the proxies of ultrafine aerosol particles. Since we are able to determine unambiguously the fraction of the clusters to which the molecules stick upon collisions, our is a purely kinetic parameter disentangling the molecule pickup from its evaporation.

Ring Formation and Hydration Effects in Electron Attachment to Misonidazole.

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.

Ionization of carboxylic acid clusters in the gas phase and on free Ar and (HO) nanoparticles: valeric acid as a model for small carboxylic acids.

We investigate ionization of valeric (n-pentanoic) acid clusters both in the gas phase and on argon and water nanoparticles using mass spectrometry. Compared to the ionization of a single valeric acid molecule, new reaction channels are observed in clusters, mostly attributed to proton transfer between two valeric acid molecules and formation of valeric anhydride. These reactions are also observed when valeric acid molecules are deposited and generate clusters on Ar, and are independent of the ionization method, whether electron ionization or photoionization is used.

Proton Transfer Reactions between Methanol and Formic Acid Deposited on Free Ar Nanoparticles.

We have sequentially picked up two astrochemically relevant Brønsted acids (methanol and formic acid) on the surface of argon nanoparticles acting as a cold support. Photoionization and electron ionization yield (HCOOH)H, (CHOH)H, and mixed protonated clusters. Experiments with perdeuterated methanol CDOD demonstrate notable proton transfer (PT) to formic acid acting as a proton acceptor in addition to the PT from formic acid which is, perhaps, a more intuitive one.

Pyruvic acid proton and hydrogen transfer reactions in clusters.

We investigate ion chemistry in pyruvic acid (PA) clusters in a molecular beam experiment. We generate two types of species, isolated (PA)N clusters and clusters deposited on large water clusters (ice nanoparticles) (PA)N·(H2O)M, M[combining macron] ≈ 390, and follow their chemistry after either 70 eV electron ionization (EI) or 193 nm UV photoionization (PI). In the (PA)N clusters, where the ionization starts with a PA molecule, both the EI and PI yield essentially the same ions: nominally (PA)nHk+, k = 1,2,3,….

Proton transfer from pinene stabilizes water clusters.

We ionize small mixed pinene-water clusters by electron impact or by using photons after sodium doping and analyze the products by mass spectrometry. Electron ionization results in the formation of pure pinene, mixed pinene-water and protonated water cluster cations. The "fragmentation free" photoionization after sodium doping results into the formation of only water-Na clusters with a mean cluster size below that observed after electron ionization.

Ionization of Ammonia Nanoices with Adsorbed Methanol Molecules.

Large ammonia clusters represent a model system of ices that are omnipresent throughout the space. The interaction of ammonia ices with other hydrogen-boding molecules such as methanol or water and their behavior upon an ionization are thus relevant in the astrochemical context. In this study, ammonia clusters (NH) with the mean size N̅ ≈ 230 were prepared in molecular beams and passed through a pickup cell in which methanol molecules were adsorbed.

Electron-triggered chemistry in HNO/HO complexes.

Polar stratospheric clouds, which consist mainly of nitric acid containing ice particles, play a pivotal role in stratospheric chemistry. We investigate mixed nitric acid-water clusters (HNO)(HO), m ≈ 1-6, n ≈ 1-15, in a laboratory molecular beam experiment using electron attachment and mass spectrometry and interpret our experiments using DFT calculations. The reactions are triggered by the attachment of free electrons (0-14 eV) which leads to subsequent intracluster ion-molecule reactions.

Clustering of Uracil Molecules on Ice Nanoparticles.

We generate a molecular beam of ice nanoparticles (HO), N̅ ≈ 130-220, which picks up several individual gas phase uracil (U) or 5-bromouracil (BrU) molecules. The mass spectra of the doped nanoparticles prove that the uracil and bromouracil molecules coagulate to clusters on the ice nanoparticles. Calculations of U and BrU monomers and dimers on the ice nanoparticles provide theoretical support for the cluster formation.

Water cluster fragmentation probed by pickup experiments.

Electron ionization is a common tool for the mass spectrometry of atomic and molecular clusters. Any cluster can be ionized efficiently by sufficiently energetic electrons, but concomitant fragmentation can seriously obstruct the goal of size-resolved detection. We present a new general method to assess the original neutral population of the cluster beam.

Photochemistry of Nitrophenol Molecules and Clusters: Intra- vs Intermolecular Hydrogen Bond Dynamics.

We investigate both experimentally and theoretically the structure and photodynamics of nitrophenol molecules and clusters, addressing the question how the molecular photodynamics can be controlled by specific inter- and intramolecular interactions. Using quantum chemical calculations, we demonstrate the structural and energetic differences between clusters of 2-nitrophenol and 4-nitrophenol, using phenol as a reference system. The calculated structures are supported by mass spectrometry.

Biomolecule Analogues 2-Hydroxypyridine and 2-Pyridone Base Pairing on Ice Nanoparticles.

Ice nanoparticles (H2O)N, N ≈ 450 generated in a molecular beam experiment pick up individual gas phase molecules of 2-hydroxypyridine and 2-pyridone (HP) evaporated in a pickup cell at temperatures between 298 and 343 K. The mass spectra of the doped nanoparticles show evidence for generation of clusters of adsorbed molecules (HP)n up to n = 8. The clusters are ionized either by 70 eV electrons or by two photons at 315 nm (3.