References of "Leyh, Bernard"
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See detailThe Vacuum UV Photoabsorption Spectrum of the Geminal Dichloroethylene (1,1-C2H2Cl2) in the 5-20 eV Range. A Vibrational Analysis of the Valence and Rydberg States.
Locht, Robert ULiege; Dehareng, Dominique; Leyh, Bernard ULiege

in Journal of Physics Communications (2017), 1

The vacuum UV photoabsorption spectrum of 1,1-C2H2Cl2 is presented and discussed in detail in the 6 - 20 eV photon energy range. The broad band observed at 6.488 eV includes the 2b1()→σ*, 2b1()→ ... [more ▼]

The vacuum UV photoabsorption spectrum of 1,1-C2H2Cl2 is presented and discussed in detail in the 6 - 20 eV photon energy range. The broad band observed at 6.488 eV includes the 2b1()→σ*, 2b1()→* valence transitions and the 2b1()→3s Rydberg transitions. A quantum chemical calculation analysis is proposed and applied to the intertwined vibrational structure belonging to these transitions. For the →σ* and →* transitions short vibrational progressions are observed, analyzed and tentatively assigned. The →3s Rydberg transition is characterized by a single progression starting at 6.746 eV. The fine structure observed between 7.5 eV and 10.1 eV has been analyzed in terms of vibronic transitions to ns- (δ= 0.89), np- (δ= 0.59 and 0.37) and nd-type (δ= 0.16) Rydberg states all converging to the 1,1-C2H2Cl2+( 2B1) ionic ground state. The vibrational structure analysis excitation leads to the following wavenumbers: ω2≈ 1310 cm-1 (162 meV), ω4≈ 650 cm-1 (81 meV) and ω5≈ 290 cm-1 (37 meV). These modes can be assigned to the C=C stretching, to the symmetric C-Cl stretching and to the symmetric Cl-C-Cl bending vibrations respectively. By the same way, eight other Rydberg states were analyzed. For the first time the vacuum UV spectrum of 1,1-C2H2Cl2 has been recorded in the 10 eV-20 eV range, revealing intense broad bands which are assigned to transitions to Rydberg states converging to excited states of 1,1-C2H2Cl2+. Assignments are also proposed for the vibrational excitations observed in this range. [less ▲]

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See detailThe Photoelectron Spectroscopy of The Dichoroetylenes: The Geminal Isomer 1,1- Cl2C2H2. An Experimental and Quantum Chemical Study.
Locht, Robert ULiege; Dehareng, Dominique; Leyh, Bernard ULiege

in Journal of Physics Communications (2017), 1

This work analyzes the threshold photoelectron spectrum (TPES) and selected Constant Ion State (CIS) spectra of the 1,1-C2H2Cl2 isomer measured using synchrotron radiation. The TPES is compared to the HeI ... [more ▼]

This work analyzes the threshold photoelectron spectrum (TPES) and selected Constant Ion State (CIS) spectra of the 1,1-C2H2Cl2 isomer measured using synchrotron radiation. The TPES is compared to the HeI-, NeI- and ArII-photoelectron spectra (PES). In the HeI-PES nine photoelectron bands have been observed at vertical ionization energies of 9.992 eV, 11.652 eV, 12.157 eV, 12.536 eV, 13.633 eV, 14.195 eV, at about 15.9 eV and 16.2 eV and at 18.496 eV successively. For most of these bands the adiabatic ionization energy could be determined and a detailed vibrational analysis of the first four bands is presented. All these bands exhibit an extended vibrational structure. In particular, the ground electronic state and the third excited state display an extended vibrational structure upon excitation by the ArII-resonance line. The assignments of the electronic bands and of the vibrational structure are based on quantum chemical calculations. These allowed us to assign the nine electronic states in terms of ionization and double excitation in a molecular orbital scheme. The good correlation between predicted vibrational wavenumbers and the experimental values allowed us to assign all observed vibrational structures. The CIS spectrum of the eight first electronic states of 1,1-C2H2Cl2+ have also been recorded. Vibrationally resolved CIS spectra of the molecular ion ground state have been obtained and are discussed. [less ▲]

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See detailLEARNING CHEMICAL KINETICS AT SECONDARY SCHOOL LEVEL: MISCONCEPTIONS AND ALTERNATIVE APPROACH
Karous, Hamad ULiege; Nihant, Brigitte ULiege; Leyh, Bernard ULiege

Conference (2017, August)

Chemical kinetics occupies a central position in describing and understanding the dynamic behaviour of matter. It is then expected that this topic shares a significant part in the teaching curricula ... [more ▼]

Chemical kinetics occupies a central position in describing and understanding the dynamic behaviour of matter. It is then expected that this topic shares a significant part in the teaching curricula. Nevertheless, the review of the scarce literature on the topic reveals that little is usually invested to adequately include this field in the major programs. Most studies demonstrate that the teaching approaches in chemical kinetics often remain limited to the qualitative macroscopic description and do not identify the necessary relevant links between the macroscopic and the submicroscopic scales. Consequently, low levels of conceptual understanding and many misconceptions can be identified at the students’ level. Based on the constructivist approach in which the learners build their own cognitive structure, a new teaching sequence including qualitative and quantitative aspects of chemical kinetics for secondary school students (15-17 years old) is proposed. This teaching sequence allows the students to develop an ability to use corpuscular models as explanatory tools as well as an adequate conceptual understanding of chemical kinetics. This approach integrates visualization tools along with active learning strategies using, e.g., interactive websites. [less ▲]

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See detailModellierung der chemischen Kinetik. Entwicklung eines Verständnisses auf molekularer Ebene anhand gezielter Versuche
Nihant, Brigitte ULiege; Karous, Hamad ULiege; Leyh, Bernard ULiege

Conference (2017, April 08)

Damit die Lernenden als zukünftige verantwortliche Bürger eine authentische Vision der Wissenschaft und ihrer Grenzen gewinnen, heben die Rahmen- und Lehrpläne immer mehr die Notwendigkeit hervor, sie mit ... [more ▼]

Damit die Lernenden als zukünftige verantwortliche Bürger eine authentische Vision der Wissenschaft und ihrer Grenzen gewinnen, heben die Rahmen- und Lehrpläne immer mehr die Notwendigkeit hervor, sie mit wissenschaftlichen Modellen und derer Erarbeitung vertraulich zu machen. Die chemische Kinetik bietet einen günstigen Rahmen, solche Modellierungskompetenzen zu fördern. Das didaktische Ziel kann wie folgt zusammengefasst werden: Eine chemische Reaktion als das Resultat wirksamer Stöße zwischen Molekülen beschreiben, um den Einfluss verschiedener experimenteller Faktoren auf die Reaktionsgeschwindigkeit zu erklären. Dies verlangt eine Modellierung, bei der die vier Ebenen (empirisch, makroskopisch, symbolisch, mikroskopisch) des didaktischen Tetraeders von Kermen und Méheut (2009) (Chemistry Education Research and Practice, 10, 24-34) erörtert werden. In diesem Vortrag werden verschiedene Aktivitäten (z.B. Versuche über molekulare Diffusion, Einführung des Begriffes des Übergangszustandes anhand angepasster, selbstgebauter Molekülmodelle) präsentiert und didaktisch ausgewertet. Großes Gewicht wird darauf gelegt, dass die Lernenden sich der erklärenden Rolle der Modelle bewusst werden, dass ihre Autonomie gefördert wird, indem der Schwierigkeitsgrad der sogenannten Zone der nächsten Entwicklung (Wygotski) entspricht, und dass das vorgestellte didaktische Modellierungsverfahren die Denkweise der Wissenschaftler reflektiert. [less ▲]

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See detailModéliser pour comprendre les phénomènes
Karous, Hamad ULiege; Nihant, Brigitte ULiege; Leyh, Bernard ULiege

Conference (2016, October 22)

Il existe actuellement un consensus sur le fait que les scientifiques ne décrivent pas la réalité telle qu’elle est dans toute sa complexité mais qu’ils en construisent des représentations qui leur ... [more ▼]

Il existe actuellement un consensus sur le fait que les scientifiques ne décrivent pas la réalité telle qu’elle est dans toute sa complexité mais qu’ils en construisent des représentations qui leur permettent de l’expliquer partiellement et de la maîtriser, partiellement également. De telles représentations sont généralement appelées des modèles et le processus de leur construction est la modélisation. Les référentiels et programmes de sciences insistent de plus en plus, dans un souci d’authenticité épistémologique, sur la nécessité de confronter les élèves aux modèles établis et à leur élaboration, afin qu’ils se constituent une vision aussi fidèle que possible de l’entreprise scientifique. Le concept de modèle possède des composantes multiples et il n’est pas aisé d’en donner une définition compacte, complète et définitive. On pourrait tenter de dire, en bref, que modéliser, c’est simplifier délibérément pour pouvoir expliquer et agir efficacement. On peut envisager différents types de modèles qui ne s’excluent pas mutuellement. On les rencontrera dans les différentes activités expérimentales que nous proposons. (i) On peut tout d’abord modéliser une situation expérimentale complexe (une pile commerciale ou un accumulateur, par exemple) par une autre situation apparentée mais plus simple et dont on contrôle mieux les paramètres, afin de mettre leur influence en lumière. Diverses expériences sur les piles (de Daniell, entre autres) illustrent cet aspect. Les expériences proposées sur la diffusion entrent également dans cette catégorie. (ii) En chimie, le principe explicatif fondamental consiste à fonder les observations macroscopiques sur des processus décrits au niveau sub-microscopique (atomes, molécules, ions, électrons). Cette représentation sub-microscopique peut être schématique et/ou symbolique. Pour plusieurs des expériences proposées, on demande de représenter schématiquement les mouvements des particules concernées. On demande aussi de traduire le phénomène en un langage symbolique, l’écriture de la réaction chimique. Ici aussi, il s’agit d’une modélisation : quand on écrit HCl(aq), par exemple, on remplace une situation complexe et relativement mal définie – des ions H3O+ et des ions Cl- hydratés avec éventuellement plusieurs couches d’hydratation – par une écriture compacte qui représente de manière conventionnelle l’essentiel de l’information dont on a besoin dans un but déterminé (un titrage, par exemple). [less ▲]

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See detailLe rôle de la compréhension de la notion de modèle dans la vision des futurs enseignants des sciences de la structure atomique
Karous, Hamad ULiege; Nihant, Brigitte ULiege; Leyh, Bernard ULiege

Conference (2016, October 16)

Atomic theory is a key concept in science education. However, it was found that students often have difficulties in learning the fundamental notions of this theory. These difficulties reveal themselves in ... [more ▼]

Atomic theory is a key concept in science education. However, it was found that students often have difficulties in learning the fundamental notions of this theory. These difficulties reveal themselves in the expression of some preconceptions which tend to persist over time and thus may occur up to the higher education level. The goal of our study is to highlight some difficulties related to the notions of models and modelling notions and to illustrate the causes of appearance of such preconceptions. To do this, two questionnaires were submitted to future sciences teachers (chemistry, biology and physics) who did a training at the University of Belgium in 2014-2015 and in 2015-2016 (40> participants). The first questionnaire deals with the modelling concept and process while the second one is about the atomic model diagrams which illustrate many textbooks. Identifying the nature of the models and their construction may lead to misconceptions while acquiring basic scientific knowledge. [less ▲]

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See detailDes pratiques enseignantes qui font obstacle au rôle des modèles dans la construction des savoirs scientifiques
Dontaine, Matthieu; Heins, Pascal ULiege; Hindryckx, Marie-Noëlle ULiege et al

Conference (2016, March)

Dans une perspective comparatiste, des didacticiens de plusieurs disciplines (biologie, chimie, histoire de l’art, mathématique et physique) ont étudié des pratiques enseignantes faisant obstacle au rôle ... [more ▼]

Dans une perspective comparatiste, des didacticiens de plusieurs disciplines (biologie, chimie, histoire de l’art, mathématique et physique) ont étudié des pratiques enseignantes faisant obstacle au rôle des modèles dans la construction des savoirs scientifiques. Leur réflexion croisée les a amenés à considérer des niveaux élevés de l’échelle de codétermination didactique de Chevallard (2012) pour identifier des indicateurs d’une certaine forme de positivisme empirique dans l’épistémologie spontanée des enseignants. Cette posture s’exprime plus ou moins différemment d’une discipline à l’autre mais le fait que les modèles et théories enseignées ont fait ou non l’objet d’une standardisation au sein de communautés scientifiques savantes déterminent fortement leur transposition didactique. De ce point de vue, l’exemple de l’histoire de l’art a joué un rôle méthodologique important permettant de contraster et de questionner les pratiques dans les autres disciplines. Ce questionnement s’inscrit dans un objectif à plus long terme qui est la reproblématisation (au sens de Orange, 2005) d’enseignements relatifs aux disciplines enseignées. [less ▲]

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See detailSmall-Angle Neutron Scattering investigation of cholesterol-doped DMPC liposomes interacting with β-cyclodextrin
Joset, Arnaud ULiege; Grammenos, Angeliki; Hoebeke, Maryse ULiege et al

in Journal of Inclusion Phenomena and Macrocyclic Chemistry (2016), 84(1), 153-161

The Small-Angle Neutron Scattering technique (SANS) has been applied to characterize the influence of a randomly methylated β–cyclodextrin (CD), called RAMEB, on dimyristoylphosphatidylcholine (DMPC ... [more ▼]

The Small-Angle Neutron Scattering technique (SANS) has been applied to characterize the influence of a randomly methylated β–cyclodextrin (CD), called RAMEB, on dimyristoylphosphatidylcholine (DMPC) liposomes doped with cholesterol. From the modelling of the experimental neutron scattering crosssections, the detailed response of the vesicle structure upon addition of increasing amounts of RAMEB up to 30 mM has been assessed. This study has been performed below and above the DMPC bilayer phase transition temperature and shows that cholesterol extraction by RAMEB is linked to a decrease of the average radius and of the aggregation number of the vesicles. This extraction takes place in a dose-dependent way until a more monodisperse population of cholesterol-free liposomes was obtained. In addition, the bilayer thickness evolution was inferred, as well as the liposome coverage by RAMEB. [less ▲]

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See detailInvestigation of the interaction between a β-cyclodextrin and DMPC liposomes: a small angle neutron scattering study
Joset, Arnaud ULiege; Grammenos, Angeliki; Hoebeke, Maryse ULiege et al

in Journal of Inclusion Phenomena and Macrocyclic Chemistry (2015), 83(3), 227-238

The Small Angle Neutron Scattering technique (SANS) has been applied to investigate the interaction between a cyclodextrin (CD) and liposomes. From the modelling of the experimental neutron scattering ... [more ▼]

The Small Angle Neutron Scattering technique (SANS) has been applied to investigate the interaction between a cyclodextrin (CD) and liposomes. From the modelling of the experimental neutron scattering cross sections, the detailed structure of dimyristoylphosphatidylcholine (DMPC) liposomes is assessed upon addition of increasing amounts of randomly methylated β-CD (RAMEB). This study has been performed at two temperatures bracketing the phase transition of the DMPC bilayers. The fraction of DMPC molecules incorporated into the vesicles is inferred. The dose-dependent phospholipidic extraction by RAMEB is quantified as well as the concomitant evolution of the liposome radius and of the thickness of the hydrophobic and hydrophilic parts of the membrane. The possible formation of CD-DMPC inclusion complexes is also assessed. The data suggest the dose-dependent coverage by RAMEB of the outer liposome interface. Our analysis highlights the important role of temperature on the mechanism of action of RAMEB. These results are discussed in the framework of the Area-Difference-Elasticity model. [less ▲]

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See detailDesigning Courses on the Nature and History of Science
Leyh, Bernard ULiege; Avitabile, Gustavo; Kelly, Orla

in Maciejowska, Iwona; Byers, Bill (Eds.) A Guidebook of Good Practice for the Pre-Service Training of Chemistry Teachers (2015)

Achieving scientific literacy is recognized as an essential goal of secondary school education. This obviously implies that science teachers, themselves, need to be scientifically literate, which in turn ... [more ▼]

Achieving scientific literacy is recognized as an essential goal of secondary school education. This obviously implies that science teachers, themselves, need to be scientifically literate, which in turn requires that emphasis should be placed on Nature of Science (NoS) issues in university pre-service (and also in-service) teacher education courses. A review of the research literature reveals that the beliefs and the understanding of teachers about NoS are often simplistic and lacking internal consistency. Research has also shown that explicit approaches towards NoS teaching are more efficient than implicit ones, and that analysis of historic cases can be an effective teaching tool. Based on an analysis of the existing literature and on their teaching experience, the authors propose a NoS curriculum for pre-service science teachers in chemistry, biology and physics and critically discuss a case example of NoS teaching practice consisting of four weekly seminars of two hours each. These seminars focus on identifying the learners’ preconceptions through team work, on discussing explicitly key NoS concepts and epistemological theories based on an inductive approach, and on highlighting the pedagogical implications. Suggestions for teaching the history of science (with emphasis on chemistry) are also provided. [less ▲]

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See detailVibronic Valence and Rydberg Transitions in Geminal Chloro-Fluoro-Ethene (1,1-C2H2FCl). A Spectroscopic and Quantum Chemical Investigation.
Locht, Robert ULiege; Dehareng, Dominique ULiege; Leyh, Bernard ULiege

in Molecular Physics (2014), 112(11), 1520-1539

The vacuum UV photoabsorption spectrum of 1,1-C2H2FCl has been examined in detail between 5 eV and 15 eV photon energy by using synchrotron radiation dispersed by three different monochromators. Quantum ... [more ▼]

The vacuum UV photoabsorption spectrum of 1,1-C2H2FCl has been examined in detail between 5 eV and 15 eV photon energy by using synchrotron radiation dispersed by three different monochromators. Quantum chemical calculations are performed to help in the analysis of the valence/Rydberg transitions region centered at 7.05 eV including the 3a”(pi)→pi* and the 3a” (pi*)→3s Rydberg transitions. Interactions between states involving transitions to the 3s, 4d and sigma* orbitals are identified. A vibrational analysis is proposed for the structures belonging to these transitions. For the pi(3a”)→pi* transition, one vibrational progression is observed with ω3=1410±50 cm-1 and its lowest excitation energy is determined at about 6.398±0.003 eV. The pi(3a”)→3s Rydberg transition is characterized by a single progression with ω3= 1410±80 cm-1 likely starting at about 6.45 eV. These vibrations are ascribed to the C=C stretching motion. The abundant structure observed in the spectrum between 7.8 eV and 10.5 eV has been analyzed in terms of vibronic transitions to ns (δ= 0.97), np (δ= 0.63 and 0.40) and nd (δ= 0.13 and -0.11) Rydberg states which belong to series converging to the 1,1-C2H2FCl+( 2A”) ionic ground state. The analysis of the vibrational structure of the individual Rydberg states has been attempted leading to average values of the wavenumbers ω3= 1 420±20 cm-1, ω7= 720±50 cm-1 and ω9= 390±50 cm-1. Between 10.5 eV and 12.5 eV nine other Rydberg states converging to the 1,1-C2H2FCl+ ( 2A') first excited state were analyzed by the same way. The vibrational structure of these Rydberg states results from the excitation of one vibrational normal mode ν7 with an average value of ω7= 520±20 cm-1 which is assigned to the C-Cl stretching vibration as inferred from quantum chemical calculations. [less ▲]

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See detailThe threshold photoelectron spectroscopy of the cis- and trans-1-chloro-2-fluoro-ethene isomers. An experimental and quantum chemical study.
Locht, Robert ULiege; Dehareng, Dominique ULiege; Leyh, Bernard ULiege

in Journal of Physics : B Atomic Molecular & Optical Physics (2014), 47(17), 175101-175012

The threshold photoelectron spectra (TPES) of the two vicinal isomers of the 1,2-C2H2FCl molecule have been investigated in the 9-24 eV energy range using synchrotron radiation. Eight (for the cis-isomer ... [more ▼]

The threshold photoelectron spectra (TPES) of the two vicinal isomers of the 1,2-C2H2FCl molecule have been investigated in the 9-24 eV energy range using synchrotron radiation. Eight (for the cis-isomer) or nine (for the trans-isomer) bands have been observed and the corresponding ionization energies have been determined. The spectroscopic assignments are based on high level quantum chemical ab initio calculations for both isomers. Most of the observed spectral features could be interpreted. For both species the first three TPES bands exhibit a rich vibrational structure. Vibrational energies were determined and assignments were also supported by quantum chemical calculations of vibrational wavenumbers for these three ionic states of both isomers. [less ▲]

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See detailThe Threshold Photoelectron Spectrum of Geminal Chloro-Fluoro-ethene (1,1-C2H2FCl) isomer. Experiment and Theory.
Locht, Robert ULiege; Dehareng, Dominique ULiege; Leyh, Bernard ULiege

in Journal of Physics : B Atomic Molecular & Optical Physics (2014), 47(8), 0851019

The threshold photoelectron spectrum (TPES) of 1,1-C2H2FCl has been measured for the first time using synchrotron radiation. It has been compared to the HeI photoelectron spectrum (PES) obtained earlier ... [more ▼]

The threshold photoelectron spectrum (TPES) of 1,1-C2H2FCl has been measured for the first time using synchrotron radiation. It has been compared to the HeI photoelectron spectrum (PES) obtained earlier [Tornow G. et al., Chem.Phys. 146 115 (1990)]. Eight photoelectron bands have been observed at 10.22 eV, 12.45 eV, 13.28 eV, 14.29 eV, 14.99 eV, 17.12 eV, 17.67 eV, and at 20.23 eV successively. Only the first three bands exhibit a rich and extensive vibrational structure. Their adiabatic ionization energies are measured and a detailed vibrational analysis is presented. The assignments of the electronic bands and of the vibrational wavenumbers were made by using ab initio quantum chemical calculations. These allowed us to provide the MO description of the eight electronic states in terms of ionization and double excitation. The good correlation between predicted vibrational wavenumbers and the experimental values provides a strong basis for the assignment of all the vibrational structures. [less ▲]

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See detailStructure of metallo-supramolecular micellar gels
Mugemana, Clément; Joset, Arnaud ULiege; Guillet, Pierre et al

in Macromolecular Chemistry and Physics (2013), 214(15), 1699-1709

A small-angle neutron scattering investigation of metallo-supramolecular micellar gels built from polystyrene-block-poly(tert-butylacrylate) PS-b-PtBA-tpy (-tpy: terpyridine) block copolymers and ... [more ▼]

A small-angle neutron scattering investigation of metallo-supramolecular micellar gels built from polystyrene-block-poly(tert-butylacrylate) PS-b-PtBA-tpy (-tpy: terpyridine) block copolymers and transition metal ions is presented. The influence of the copolymer concentration on the structure and spatial organization of the micelles, as well as the impact of the subsequent addition of metal ions (Fe(II), Ni(II), and Zn(II)) on these characteristics is extensively studied. The experimental scattering cross-sections are fitted with an analytical formula based on the Percus–Yevick hard-sphere model and on the Pedersen–Gerstenberg model for the structure and the form factor, respectively. The resulting structural information is correlated with previously performed light scattering and rheology experiments. [less ▲]

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See detailMetallo-supramolecular micellar gels: a structural study
Mugemana, Clément; Joset, Arnaud ULiege; Guillet, Pierre et al

Poster (2013, July 10)

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See detailMetallo-supramolecular micellar gels: a structural study
Mugemana, Clément; Joset, Arnaud ULiege; Guillet, Pierre et al

Conference (2013, May 17)

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See detailIon Dissociation Kinetics in Mass Spectrometry
Leyh, Bernard ULiege

in Reedijk, J. (Ed.) Reference Module in Chemistry, Molecular Sciences and Chemical Engineering (2013)

The variation of fragmentation rate constants as a function of the parent ion internal energy, or, alternatively, as a function of temperature, is crucial information to unravel the dissociation ... [more ▼]

The variation of fragmentation rate constants as a function of the parent ion internal energy, or, alternatively, as a function of temperature, is crucial information to unravel the dissociation mechanisms of molecular ions. This contribution provides the reader first with basic information on the statistical theories used to model unimolecular rate constants. Various experimental methods to measure such rate constants in the 102 to 1010 s^(-1) range are then discussed. Kinetic isotope effects are also briefly dealt with. How reaction mechanisms can be inferred from kinetic data is handled in an extensive section where selected examples from the recent literature are discussed. [less ▲]

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