arXiv subjects

Wania Wolff

Publications and source records attributed to Wania Wolff.

5 recordsLinked to original sources

arXiv2025

Glow discharge induced reactions in mixtures of ozone and chlorodifluoromethane with atmospheric gases

The influence of extraterrestrial particles like cosmic radiation (CR) on the chemistry and ozone density in the Earth stratosphere is not well investigated and normally neglected in stratospheric chemistry models. Here we present the commissioning of a lab-based apparatus which aims at simulating conditions in the stratosphere in order to get better insight into the reactions induced by the secondary-particle showers from high-energetic CR which can reach low altitudes. Admixtures of ozone and the halocarbon CHClF2 (R22, chlorodifluoromethane) to atmospheric gases (N2, O2, Ar) were exposed to a glow discharge in the total pressure regime of a few hPa. According to the mass spectrometric analysis of the gas composition the discharge initiates significant ozone depletion by a factor four in the absence of R22. This depletion is strongly enhanced to two orders of magnitude in the presence of R22. The possible underlying reactions are discussed.

physics.plasm-ph↗

arXiv2023

Adaptable platform for trapped cold electrons, hydrogen and lithium anions and cations

Cold cations, electrons and anions are ubiquitous in space, participate in star formation chemistry and are relevant to studies on the origin of molecular biology homochirality. We report on a system to generate and trap these species in the laboratory. Laser ablation of a solid target (LiH) facing a sublimating Ne matrix generates cold electrons, anions, and cations. Axial energy distributions (of e$^-$, H$^\pm$ and Li$^\pm$) peaked at 0-25 meV are obtained in a Penning trap at 90 mT and 0.5 eV barrier. Anions can be guided and neutralized with low recoil energy by near-threshold photodetachment. An immediate prospect for this H$^-$ source is to load hydrogen atoms into the ALPHA antihydrogen trap at CERN towards direct spectroscopic comparison of both conjugated species beyond 13 significant figures. The production is potentially scalable and adaptable to different species including deuterium and tritium, relevant for neutrino mass and fusion research.

physics.atom-ph↗

arXiv2019

Low-temperature chemistry induced by cosmic rays: positive and negative ions desorption from nitrile-bearing astrophysical ice analogues

In cold core of dark molecular clouds, where the UV radiation from external sources is strongly attenuated, cosmic rays can induce chemical reactions on the surface of ice-covered grains promoting the ejection of the processed material to the gas phase. We report the positive and negative secondary ion emission from pure CH3CN, C2H3CN and i-C3H7CN ices due to the bombardment of heavy ions (252Cf fission fragments), simulating the incidence of cosmic rays onto icy surfaces. The secondary ions emitted from each sample were analysed by time-of-flight mass spectrometry (TOF-MS), using Plasma Desorption Mass Spectrometry (PDMS) technique. Several ionic species were identified, indicating strong fragmentation on the frozen surface. Proton-transfer processes are suggested to play a role for positive ion desorption, as evidenced by the protonated RCNH+ parent molecules and (RCN)nH+ ionic clusters. The high electron affinity of the cyano radical seems to contribute to the strong emission of CN-, as well as anions attributed to the CHmCN- fragment and (RCN)nCN- cluster series. Sputtering and desorption of ion clusters (positive and negative) induced by heavy ion bombardment are suggested to constitute a route by which new neutral or ionised molecular species may be delivered to the gas phase where thermal desorption is negligible.

astro-ph.SR↗

arXiv2019

Destruction and multiple ionization of PAHs by X-rays in circumnuclear regions of AGNs

The infrared signatures of polycyclic aromatic hydrocarbons (PAHs) are observed in a variety of astrophysical objects, including the circumnuclear medium of active galactic nuclei (AGNs). These are sources of highly energetic photons (0.2 to 10 keV), exposing the PAHs to a harsh environment. In this work, we examined experimentally the photoionization and photostability of naphthalene (C$_{10}$H$_{8}$), anthracene (C$_{14}$H$_{10}$), 2-methyl-anthracene (C$_{14}$H$_{9}$CH$_{3}$) and pyrene (C$_{16}$H$_{10}$) upon interaction with photons of 275, 310 and 2500 eV. The measurements were performed at the Brazilian Synchrotron Light Laboratory using time-of-flight mass-spectrometry (TOF-MS). We determined the absolute photoionization and photodissociation cross sections as a function of the incident photon energy; the production rates of singly, doubly and triply charged ions; and the molecular half-lives in regions surrounding AGNs. Even considering moderate X-ray optical depth values ($τ= 4.45$) due to attenuation by the dusty torus, the half-lives are not long enough to account for PAH detection. Our results suggest that a more sophisticated interplay between PAHs and dust grains should be present in order to circumvent molecular destruction. We could not see any significant difference in the half-life values by increasing the size of the PAH carbon backbone, N$_C$, from 10 to 16. However, we show that the multiple photoionization rates are significantly greater than the single ones, irrespective of the AGN source. We suggest that an enrichment of multiply charged ions caused by X-rays can occur in AGNs.

astro-ph.GA↗

arXiv2014

Slow ground state molecules from matrix isolation sublimation

We describe the generation and properties of a cryogenic beam of $^7$Li$_2$ dimers from sublimation of a neon matrix where lithium atoms have been implanted via laser ablation of solid precursors of metallic lithium or lithium hydride (LiH). Different sublimation regimes lead to pulsed molecular beams with different temperatures, densities and forward velocities. With laser absorption spectroscopy these parameters were measured using the molecular $^7$Li$_2$ (R) transitions A$^1Σ_u^+(v'=4,J'=J''+1)\leftarrow $X$^1Σ_g^+ (v''=0,J''=0,1,3)$. In a typical regime, sublimating a matrix at 16 K, translational temperatures of 6--8 K with a drift velocity of 130 m$\,$s$^{-1}$ in a free expanding pulsed beam with molecular density of 10$^9$ cm$^{-3}$, averaged along the laser axis, were observed. Rotational temperatures around 5--7 K were obtained. In recent experiments we were able to monitor the atomic Li signal -- in the D2 line -- concomitantly with the molecular signal in order to compare them as a function of the number of ablation pulses. Based on the data and a simple model, we discuss the possibility that a fraction of these molecules are being formed in the matrix, by mating atoms from different ablation pulses, which would open up the way to formation of other more interesting and difficult molecules to be studied at low temperatures. Such a source of cryogenic molecules have possible applications encompassing fundamental physics tests, quantum information studies, cold collisions, chemistry, and trapping.

physics.atom-ph↗