Sylvain Laube

The dissociative recombination of hydrocarbon ions. I. Light alkanes

Rate coefficients for the dissociative recombination of a series of hydrocarbon ions derived from normal alkanes have been measured using the FALP-MS technique. Despite the increasing complexity of the ions along the series, the measured rate coefficients are found to be remarkably similar having values between 5.5 and 8.3×10−7 cm3 s−1.

New FALP-MS measurements of , and dissociative recombination

A series of measurements of the rate coefficient for the dissociative recombination (DR) of has been recorded. A value of was found for ions that are vibrationally cold. This is somewhat smaller than that measured previously by this group. The difference is ascribed to aerodynamic effects which affected our earlier measurement that have been eliminated in the present work. Results for and DR are also reported.

The dissociative recombination of NO+: the influence of the vibrational excitation state

The dissociative recombination rate coefficient for NO+ has been measured at 300 K using a flowing afterglow Langmuir probe-mass spectrometer apparatus. A value of (4±1) × 10-7 cm3 s-1 has been found for ground electronic and vibrational state ions produced from the parent NO gas. Ions produced from a N2:O2 mixture which are in a wide range of vibrationally excited states display a smaller recombination rate of (1.6±0.5) × 10-7 cm3 s-1.

Electron attachment to anthracene. A FALP measurement of the rate coefficient at room temperature

The rate coefficient β for electron attachment to anthracene has been measured at room temperature using a flowing afterglow Langmuir probe mass spectrometer. A value of 1 × 10−9 cm3 s−1 (30% uncertainty) was found, indicating that an activation energy barrier might exist.

The dissociative recombination of hydrocarbon ions. III. Methyl-substituted benzene ring compounds

The recombination of electrons with cyclic ions produced via ion – molecule reactions between atomic precursor ions and methyl-substituted benzene ring compounds (toluene , ortho-, and para-xylene and mesitylene) has been studied at 300 K using a flowing afterglow Langmuir probe-mass spectrometer apparatus. Differing amounts of energy can be deposited into the daughter ions depending upon which atomic precursor is used. It has been found that same-mass daughter ions formed from different precursors displayed different recombination rate coefficients indicating that different isomeric forms were reacting. In particular , the benzene ring of the toluene cation expands to a seven-membered ring following isomerization to the cycloheptatriene form. H atom abstraction allows two different isomeric daughter ions to be formed that do not interconvert and that display different recombination rates. A similar behavior was observed for the xylenes and for mesitylene. All recombination rates lie in the range from 10-7 to 10 -6 cm3 s-1 and display no apparent relation with size nor with the aromaticity of the ions .

Reaction of anthracene with atomic ions of interstellar interest. A FALP measurement at room temperature

We present the results obtained on studying the reaction of anthracene with some atomic ions of interstellar interest (He+ and C+) and with Ar+. Rate coefficients have been measured at room temperature (293 K) in afterglow experiments using flowing afterglow Langmuir probe-mass spectrometer apparatus. Reactions proceed with rate coefficients of respectively 5.2 × 10−9, 3 × 10−9, 1 × 10−9 cm3 s−1 for He+, C+ and Ar+. The results were obtained with an uncertainty of about 30% and were found to be close to the Langevin rate. The nature of the products has also been investigated. More particularly, the evidence for carbon accretion and for the production of doubly charged species is discussed.

Experimental and theoretical study of intramultiplet transitions in collisions of C(3P) and Si(3P) with He

We present a combined theoretical and experimental study of intramultiplet transitions in collisions of C(3P) and Si(3P) with He. Relaxation rate constants have been measured using the CRESU (Cinetique de Reaction en Ecoulement Supersonique Uniforme) technique at 15 K for C(3P)+He and over the 15–49 K temperature range for Si(3P)+He. Three sets of interaction potentials have been generated for the 3∑− and 3∏ electronic states of CHe and SiHe systems. Quantum-mechanical calculations have been performed on these potential curves for the spin–orbit relaxation and excitation. Cross sections and rate constants are very sensitive to the interaction potential. For the Si(3P)+He system, an overall good agreement between the theoretical and experimental rate constants is found with the best quality interaction potential, while for the C(3P)+He system experimental rate constants are much smaller than the theoretical ones.

A Didactic-based Model of Scenarios for Designing an Adaptive and Context-Aware Learning System

Nowadays, technology-enhanced learning systems must have the ability to deal with the context and to allow dynamic adaptation based on pedagogical theories and knowledge models. The main issue is to design a generic scenario to deal with the broadest range of learning situations. From a generic scenario, the learning system will compute on the fly a scenario adapted to the current learner and its situation. Our main contribution is a semantic and didactic-based model of scenarios to design an adaptive and context- aware learning system. The scenario model is acquired from: i) the know-how and real practices of teachers ii) the theory in didactic anthropology of knowledge of Chevallard [1]; iii) a hierarchical task model.

The dissociative recombination of and

The dissociative recombination of and has been studied using a FALP-MS technique. is found to have a small recombination rate while that of is at 300 K.

The Co-Design of Scenarios for a Didactic-based E-learning System viewed as an Adaptive Virtual Document

The design and engineering of e-learning systems must be considered as a transdisciplinary problem requiring the integration of different scientific approaches. The design process of e-learning systems needs to consider several theories, models and artifacts - the e-learning system. We claim it is essential to ensure the traceability and the interpretation of phenomena related to the use of artifacts in studying precisely the relationships between theories, models and artifacts. Consequently, we develop a co-design methodology to deal with these goals. The main contribution of this paper is to describe a methodological approach enabling the co-design of problem-based learning scenarios in sciences which are based on teacher real practices acquired by means of the theory in didactic anthropology of knowledge and to show why we can formalize them in a hierarchical task model to design an adaptive e-learning system