Ion Coulomb crystals: from quantum technology to chemistry close to the absolute zero point

Dulieu, O.; Willitsch, Stefan

doi:10.1051/epn/2017203

Cited by 7 publications

(10 citation statements)

References 13 publications

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“…Anisotropic intermolecular forces, associated with alignment and orientation effects produced by atomic and molecular polarization, modulate the fate of molecular collisions. A knowledge of these phenomena is relevant to control the stereodynamics of elementary processes occurring in the gas phase and at the gas–surface interface, − but a general theoretical and computational foundation is still lacking.…”

Section: Introductionmentioning

confidence: 99%

Quantum-State Controlled Reaction Channels in Chemi-ionization Processes: Radiative (Optical–Physical) and Exchange (Oxidative–Chemical) Mechanisms

et al. 2020

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Conspectus Most chemical processes are triggered by electron or charge transfer phenomena (CT). An important class of processes involving CT are chemi-ionization reactions. Such processes are very common in nature, involving neutral species in ground or excited electronic states with sufficient energy (X*) to yield ionic products, and are considered as the primary initial step in flames. They are characterized by pronounced electronic rearrangements that take place within the collisional complex (X···M)* formed by approaching reagents, as shown by the following scheme, where M is an atomic or molecular target: X* + M → (X···M)* → [(X+···M) ↔ (X···M+)] e− (X···M)+ + e– → final ions. Despite their important role in fundamental and applied research, combustion, plasmas, and astrochemistry, a unifying description of these basic processes is still lacking. This Account describes a new general theoretical methodology that demonstrates, for the first time, that chemi-ionization reactions are prototypes of gas phase oxidation processes occurring via two different microscopic mechanisms whose relative importance varies with collision energy, E c, and separation distance, R. These mechanisms are illustrated for simple collisions involving Ne*(3P2,0) and noble gases (Ng). In thermal and hyperthermal collisions probing interactions at intermediate and short R, the transition state [(Ne···Ng)+] e− is a molecular species described as a molecular ion core with an orbiting Rydberg electron in which the neon reagent behaves as a halogen atom (i.e., F) with high electron affinity promoting chemical oxidation. Conversely, subthermal collisions favor a different reaction mechanism: Ng chemi-ionization proceeds through another transition state [Ne*······Ng], a weakly bound diatomic-lengthened complex where Ne* reagent, behaving as a Na atom, loses its metastability and stimulates an electron ejection from M by a concerted emission–absorption of a “virtual” photon. This is a physical radiative mechanism promoting an effective photoionization. In the thermal regime of E c, there is a competition between these two mechanisms. The proposed method overcomes previous approaches for the following reasons: (1) it is consistent with all assumptions invoked in previous theoretical descriptions dating back to 1970; (2) it provides a simple and general description able to reproduce the main experimental results from our and other laboratories during last 40 years; (3) it demonstrates that the two “exchange” and “radiative” mechanisms are simultaneously present with relative weights that change with E c (this viewpoint highlights the fact that the “canonical” chemical oxidation process, dominant at high E c, changes its nature in the subthermal regime to a direct photoionization process; therefore, it clarifies differences between the cold chemistry of terrestrial and interstellar environments and the energetic one of combustion and flames); (4) the proposed method explicitly accounts for the influence of the degree of valence orbital alignmen...

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Section: Introductionmentioning

confidence: 99%

Quantum-State Controlled Reaction Channels in Chemi-ionization Processes: Radiative (Optical–Physical) and Exchange (Oxidative–Chemical) Mechanisms

et al. 2020

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“…This highlights the fact that that the “canonical” chemical oxidation process, dominant at a high collision energy, changes its nature in the subthermal regime to a pure direct photoionization process . It also points out differences between the cold chemistry of terrestrial and interstellar environments and the hot one of combustion and flames. − ,, …”

Section: Discussionmentioning

confidence: 90%

“…Recently, we developed and applied a new/original method − to the detailed investigation of chemi-ionization reactions (CHEMI), promoted by collisions of atoms electronically excited in metastable states with other atoms, that are prototypical of barrierless processes leading to the formation of ionic products plus electrons. − The study of them remains of great interest for fundamental and applied research, since it allows a definition of the role of the barrierless reactions in cold chemistry − and an opportunity to model energy-transfer phenomena occurring in flames, plasmas, and electric discharges. , …”

Section: Introductionmentioning

confidence: 99%

Chemi-Ionization Reactions and Basic Stereodynamical Effects in Collisions of Atom-Molecule Reagents

et al. 2021

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A new theoretical method, developed by our laboratory to describe the microscopic dynamics of gas-phase elementary chemi-ionization reactions, has been applied recently to study prototype atom–atom processes involving reactions between electronically excited metastable Ne*( 3 P 2,0 ) and heavier noble gas atoms. Important aspects of electronic rearrangement selectivity have been emphasized that suggested the existence of two fundamental microscopic reaction mechanisms. The distinct mechanisms, which are controlled by intermolecular forces of chemical and noncovalent nature respectively, emerge under different conditions, and their balance depends on the collision energy regime investigated. The present paper provides the first step for the extension of the method to cases involving molecules of increasing complexity, whose chemi-ionization reactions are of relevance in several fields of basic and applied researches. The focus is here on the reactions of Ne* with simple inorganic molecules as Cl 2 and NH 3 , and the application of the method discloses relevant features of the reaction microscopic evolution. In particular, this study shows that the balance of two fundamental reaction mechanisms depends not only on the collision energy and on the relative orientation of reagents but also on the orbital angular momentum of each collision complex. The additional insights so emphasized are of general relevance to assess in detail the stereodynamics of many other elementary processes.

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“…At present, particular attention is devoted to basic phenomena occurring both at very low temperature (see for instance Refs. [7][8][9][10][11][12]), of interest for the quantum behavior of matter and for the balance of elementary processes occurring in interstellar media, and at room and higher temperature, of relevance for the chemistry and physics of planetary atmospheres and plasmas [13][14][15]. The final target of this challenge is the full characterization of all crucial effects (basic quantities), controlling, under a variety of conditions of interest, the stereo-dynamical evolution of each elementary process.…”

Section: Introductionmentioning

confidence: 99%

The selective role of the orbital angular momentum on the reaction stereo-dynamics

et al. 2023

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This paper reports on the characterization of the stereo-dynamic controlling three different chemi-ionization reactions, recent objective of our study, since they participate to the balance of phenomena occurring in plasma, interstellar medium, planetary atmospheres, flames and lasers. The optical potential, obtained by a phenomenological method and defined in the whole space of the relative configurations of reagents, has been formulated in an accurate and internally consistent way for three different systems. Some cuts of the multidimensional potential, that asymptotically correlate with a specific fine level of the open shell atom and/or with a defined orientation of the molecular reagent, have been exploited in the present study to emphasize crucial features of the collision dynamics along selected entrance channels of the reactions. Consistently, basic quantities determining the topology of the reaction stereo-dynamics have been properly defined, emphasizing in the three cases relevant changes in the microscopic reaction evolution. Much attention focused on the selectivity of the orbital angular momentum, affecting each collision event at any chosen collision energy. It controls the relative weight of two different reaction mechanisms. The direct reaction mechanism is driven by short-range chemical forces, promoting, by direct electron transfer between reagents, a prototypical elementary oxidation reaction. The indirect mechanism, controlled by the combination of long-range chemical and physical forces, can be triggered by a virtual photon exchanged between reagents, promoting a sort of photo-ionization process. Obtained results and emphasized differences appear to be of general interest for many other elementary processes, more difficult to characterize at this level of detail. Graphic abstract

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Ion Coulomb crystals: from quantum technology to chemistry close to the absolute zero point

Cited by 7 publications

References 13 publications

Quantum-State Controlled Reaction Channels in Chemi-ionization Processes: Radiative (Optical–Physical) and Exchange (Oxidative–Chemical) Mechanisms

Quantum-State Controlled Reaction Channels in Chemi-ionization Processes: Radiative (Optical–Physical) and Exchange (Oxidative–Chemical) Mechanisms

Chemi-Ionization Reactions and Basic Stereodynamical Effects in Collisions of Atom-Molecule Reagents

The selective role of the orbital angular momentum on the reaction stereo-dynamics

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