Publications by authors named "Henning T Schmidt"
Article Synopsis
- The study investigates the reaction between vibronically cold NO^{+} and O^{-} at a low collision energy of about 0.1 eV, focusing on single-collision interactions.
- The reaction primarily results in the formation of three ground-state atomic fragments.
- Using product-momentum analysis, the researchers propose a two-step mechanism where the anion donates an electron, leading to an intermediate Rydberg state of NO that eventually breaks apart.
Article Synopsis
- The study focuses on the mutual neutralization reaction between hydronium (HO) and hydroxide (OH) ions, which is a basic yet not well-understood chemical process.
- Using advanced imaging techniques in a cryogenic ion storage facility, researchers observed the products formed during these reactions at low collision energies.
- The findings reveal that most of the reactions involve electron-transfer mechanisms, while some also involve proton transfer, helping to create a basis for future modeling of charge-transfer processes.
Article Synopsis
- Recent observations have detected small Polycyclic Aromatic Hydrocarbons (PAHs) in the Taurus Molecular Cloud using radio telescopes, presenting challenges for astrochemical modeling of their abundance.
- The study finds that the rapid cooling of ionized PAHs through a process called Recurrent Fluorescence (RF) stabilizes these molecules, aiding their survival in space.
- Researchers employed a novel experimental method to accurately measure the cooling rate of the 1-cyanonaphthalene cation, supporting previous calculations and emphasizing the need for enhanced models to better understand PAHs in astronomical contexts.*
Article Synopsis
- Naphthalene and azulene are isomeric polycyclic aromatic hydrocarbons being studied for their presence in the Taurus Molecular Cloud-1, particularly focusing on how they transform under thermal and photo-induced conditions.
- Research using a cryogenic electrostatic ion storage ring revealed rapid isomerization and a quasi-equilibrium between naphthalene and azulene radical cations, impacting their dissociation pathways.
- The findings highlight efficient radiative cooling mechanisms that may imply the greater abundance of small cations like naphthalene in space, with potential applications for studying other PAHs' behaviors.
Article Synopsis
- The study investigates the recurrent fluorescence (RF) cooling rates of tetracene cations at varying internal energies and storage times using two different ion-beam storage rings: the cryogenic DESIREE in Stockholm and the room temperature Mini-Ring in Lyon.
- Measured RF cooling rates range from 150 to 1000 seconds for internal energies between 7 to 9.4 eV, showing significantly more efficient cooling compared to smaller polycyclic aromatic hydrocarbons (PAHs) like anthracene and naphthalene.
- The complementary characteristics of both rings enable broader measurements of RF rates, with Mini-Ring focusing on faster-decaying hotter ions and DESIREE targeting slower-decaying colder ions, resulting in
Article Synopsis
- The article DOI: 10.1103/PhysRevLett.128.033401 has been updated or amended.
- The corrections are important for accurate interpretation of the research findings.
- Readers should refer to the corrected version for the most reliable information.
Article Synopsis
- * The research focuses on the cationic form of 1-CNN, analyzing its unimolecular dissociation and radiative cooling rates through experiments that mimic interstellar conditions.
- * Findings show that a process called Recurrent Fluorescence helps stabilize 1-CNN, which suggests that small PAHs might not be destroyed as quickly in space as commonly believed.
Article Synopsis
- The study investigates the cooling characteristics of linear hydrocarbon anions CH and CH using a specialized cryogenic experiment that monitors their photodetachment action spectra.
- The average cooling rates for these ions were measured and found to be 19 ± 2 seconds for CH and 3.0 ± 0.2 seconds for CH, using a technique called Non-negative Matrix Factorization.
- The cooling dynamics observed provide valuable insights for understanding the thermal properties of these anions and improving models related to their behavior in astrochemical settings.
Article Synopsis
- Negative ions play a crucial role in various scientific fields such as interstellar chemistry and anti-matter research, where their unique properties are influenced by electron-correlation effects.
- Traditional methods for studying these ions face challenges due to their loosely bound nature and limited optical transitions, hindering high-resolution detection techniques.
- A new method has been developed that accurately measures negative ion binding energies with significantly higher precision, utilizing laser manipulation and a cryogenic ion-beam storage ring, leading to a reported electron affinity of 1.461 112 972(87) eV for oxygen.
Article Synopsis
- Researchers examined how HfF and WF molecular anions decay spontaneously and when exposed to different laser wavelengths in a specialized facility called DESIREE, observing these processes over long time scales thanks to very low temperatures and pressures.
- The study found that both anions experience decay through electron detachment or fragmentation, with WF anions showing a significant increase in neutralization at a specific energy threshold of about 3.5 eV, while HfF did not exhibit any enhancement in neutrons produced, even at high energy levels.
- This finding could aid in improving the detection of the rare isotope Hf in accelerator mass spectrometry by minimizing interference from stable isobar W, which is important for astrophysical studies on nucleosynthesis
Article Synopsis
- The study measures the statistical vibrational autodetachment (VAD) and radiative cooling rates of isolated benzoquinone radical anions using a cryogenic ion storage facility.
- VAD rates were determined through time-dependent yield measurements of neutral benzoquinone from spontaneously emitting electrons and were affected by radiative cooling after about 11 ms.
- The research also involved measuring the radiative cooling rate of benzoquinone over 0.5 s, linking findings to vibrational temperatures and discussing implications for astrochemistry.
Article Synopsis
- - The study investigates how Mg atoms are generated from reactions between Mg^{+} and D^{-} at low collision energies (around 59 meV) using a specific experimental method.
- - The results show significant differences when compared to previous full-quantum theories, indicating that past calculations have underestimated the total reaction rate by nearly double in low-energy scenarios.
- - The researchers suggest that using asymptotic model calculations provides more accurate results and advocate for applying this approach to study more complicated systems, which is important for understanding stellar conditions.
Article Synopsis
- Laboratory experiments help us understand the interstellar medium (ISM), but matching lab findings with cosmic reactions is challenging due to different timescales.
- This study focuses on the reactive fragments of coronene, a type of polycyclic aromatic hydrocarbon (PAH), after they collide with helium atoms at high speeds.
- Results indicate that these damaged PAH fragments can remain stable and influential in the ISM over long periods, potentially affecting interstellar chemistry due to their enhanced reactivity.
The mutual neutralisation of O with O has been studied in a double ion-beam storage ring with combined merged-beams, imaging and timing techniques. Branching ratios were measured at the collision energies of 55, 75 and 170 (± 15) meV, and found to be in good agreement with previous single-pass merged-beams experimental results at 7 meV collision energy. Several previously unidentified spectral features were found to correspond to mutual neutralisation channels of the first metastable state of the cation (O(D), ≈ 3.
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- The study investigates how perylene cations fragment over time, measuring these processes in a cryogenic ion storage ring for up to 2 seconds.
- A quantitative model of fragmentation is proposed, which considers both fragmentation and radiative cooling, showing good agreement with experimental data, especially when accounting for daughter ions.
- The research quantifies important optical properties of perylene, determining the strength of specific electronic transitions and how they relate to cooling processes, which are crucial for improving models of astrochemistry.
Article Synopsis
- Researchers at Stockholm University's DESIREE facility measured the cooling lifetimes and detachment energies for three sizes of carbon anions (C3, C4, and C5) in a super-cool environment with low pressure.
- They created two-dimensional photodetachment spectra that showed how the anions lost energy over time, revealing cooling lifetimes of 3.1 s, 6.8 s, and 24 s for each respective anion size.
- The study's findings confirmed the occurrence of radiative cooling and established a model for simulating cooling dynamics, which could be useful for exploring other molecular anions in future research.
The multi-photon photodissociation action spectrum of the coronene cation (C24H12+) has been measured in the cryogenic electrostatic storage ring DESIREE (Double ElectroStatic Ion Ring ExpEriment) as a function of storage time. These measurements reveal not only the intrinsic absorption profile of isolated coronene cations, but also the rate at which hot-band absorptions are quenched by radiative cooling. Just after injection, the action spectrum is severely reddened by hot-band absorptions.
View Article and Find Full Text PDFKnockout driven fragmentation of porphyrins.
Phys Chem Chem Phys
August 2017
We have studied collisions between tetraphenylporphyrin cations and He or Ne at center-of-mass energies in the range 50-110 eV. The experimental results were interpreted in view of density functional theory calculations of dissociation energies and classical molecular dynamics simulations of how the molecules respond to the He/Ne impact. We demonstrate that prompt atom knockout strongly contributes to the total destruction cross sections.
View Article and Find Full Text PDFDouble-core-hole spectroscopy for chemical analysis with an intense X-ray femtosecond laser.
Proc Natl Acad Sci U S A
October 2011
Theory predicts that double-core-hole (DCH) spectroscopy can provide a new powerful means of differentiating between similar chemical systems with a sensitivity not hitherto possible. Although DCH ionization on a single site in molecules was recently measured with double- and single-photon absorption, double-core holes with single vacancies on two different sites, allowing unambiguous chemical analysis, have remained elusive. Here we report that direct observation of double-core holes with single vacancies on two different sites produced via sequential two-photon absorption, using short, intense X-ray pulses from the Linac Coherent Light Source free-electron laser and compare it with theoretical modeling.
View Article and Find Full Text PDFOn the hydrogen loss from protonated nucleobases after electronic excitation or collisional electron capture.
Eur J Mass Spectrom (Chichester)
February 2010
In this work, we have subjected protonated nucleobases MH(+) (M = guanine, adenine, thymine, uracil and cytosine) to a range of experiments that involve high-energy (50 keV) collision induced dissociation and electron capture induced dissociation. In the latter case, both neutralisation reionisation and charge reversal were done. For the collision induced dissociation experiments, the ions interacted with O(2).
View Article and Find Full Text PDFThe results from an experimental study of bare and microsolvated peptide monocations in high-energy collisions with cesium vapor are reported. Neutral radicals form after electron capture from cesium, which decay by H loss, NH(3) loss, or N-C(alpha) bond cleavage into characteristic z(*) and c fragments. The neutral fragments are converted into negatively charged species in a second collision with cesium and are identified by means of mass spectrometry.
View Article and Find Full Text PDFAn assembly consisting of a stack of three microchannel plates (MCPs) and a phosphor screen anode has been operated over the temperature range from 300 to 12 K. We report on measurements at 6.4 kHz (using an alpha source) and with dark counts only (15 Hz).
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