Publications by authors named "MingChao Ji"
The radiative cooling of naphthalene dimer cations, (CH) was studied experimentally through action spectroscopy using two different electrostatic ion-beam storage rings, DESIREE in Stockholm and Mini-Ring in Lyon. The spectral characteristics of the charge resonance (CR) band were observed to vary significantly with a storage time of up to 30 seconds in DESIREE. In particular, the position of the CR band shifts to the blue, with specific times (inverse of rates) of 0.
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- 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.
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- 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.
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- 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.*
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- 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.
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- 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
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- 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.
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- * 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.
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- 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
The unimolecular dissociation and infrared radiative cooling rates of cationic 1-hydroxypyrene (OHPyr, CHO) and 1-bromopyrene (BrPyr, CHBr) are measured using a cryogenic electrostatic ion beam storage ring. A novel numerical approach is developed to analyze the time dependence of the dissociation rate and to determine the absolute scaling of the radiative cooling rate coefficient. The model results show that radiative cooling competes with dissociation below the critical total vibrational energies E = 5.
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- - 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.
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- 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.
This work presents a study of the thermal evaporation and stability of pyrene (CH) clusters. Thermal evaporation rates of positively charged mass-selected clusters are measured for sizes in the range n = 3-40 pyrene units. The experimental setup consists of a gas aggregation source, a thermalization chamber, and a time of flight mass spectrometer.
View Article and Find Full Text PDFIn cosmic environments, polycyclic aromatic hydrocarbons (PAHs) strongly interact with vacuum ultraviolet (VUV) photons emitted by young stars. Trapped PAH cations ranging in size from 30 to 48 carbon atoms were irradiated by tunable synchrotron light (DESIRS beamline at SOLEIL). Their ionization and dissociation cross sections were determined and compared with TD-DFT computed photoabsorption cross sections.
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