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See detailSelf-assembly of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers in aqueous solution
Vangeyte, Pattrick; Leyh, Bernard ULg; Heinrich, M. et al

in Langmuir (2004), 20(20), 8442-8451

The associative behavior of monodisperse diblock copolymers consisting of a hydrophilic poly(ethylene oxide) block and a hydrophobic poly(epsilon-caprolactone) or poly(gamma-methyl-epsilon-caprolactone ... [more ▼]

The associative behavior of monodisperse diblock copolymers consisting of a hydrophilic poly(ethylene oxide) block and a hydrophobic poly(epsilon-caprolactone) or poly(gamma-methyl-epsilon-caprolactone) block has been studied in aqueous solution. Copolymers have been directly dissolved in water. The solution properties have been studied by surface tension, in relation to mesoscopic analyses by NMR (self-diffusion coefficients), transmission electron microscopy, and small-angle neutron and X-ray scattering. The experimental results suggest that micellization occurs at low concentration (approximately 0.002 wt %) and results in a mixture of unimers and spherical micelles that exchange slowly. The radius of the micelles has been measured (ca. 11 nm), and the micellar substructure has been extracted from the fitting of the SANS data with two analytical models. The core radius and the aggregation number change with the hydrophobic block length according to scaling laws as reported in the scientific literature. The poly(ethylene oxide) blocks are in a moderately extended conformation in the corona, which corresponds to about 25% of the completely extended chain. No significant modification is observed when poly(gamma-methyl-epsilon-caprolactone) replaces poly(epsilon-caprolactone) in the diblocks. [less ▲]

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See detailSelf-assembling of poly(-caprolactone)-b-poly(ethylene oxide) diblock copolymers in aqueous solution and at the silica–water interface
Leyh, Bernard ULg; Vangeyte, Patrick; Heinrich, M. et al

in Physica B: Condensed Matter (2004), 350(1-3, suppl. 1), 901-904

Small-angle neutron scattering is used to investigate the self-assembling behaviour of poly( ε-caprolactone)-b-poly(ethylene oxide) diblock copolymers with various block lengths (i) in aqueous solution ... [more ▼]

Small-angle neutron scattering is used to investigate the self-assembling behaviour of poly( ε-caprolactone)-b-poly(ethylene oxide) diblock copolymers with various block lengths (i) in aqueous solution, (ii) in aqueous solution with the addition of sodium dodecyl sulphate (SDS) and (iii) at the silica-water interface. Micelles are observed under our experimental conditions due to the very small critical micellar concentration of these copolymers (0.01 g/l). The poly( ε-caprolactone) core is surrounded by a poly(ethylene oxide) corona. The micellar form factors have been measured at low copolymer concentrations (0.2 wt%) under selected contrast matching conditions. The data have been fitted to various analytical models to extract the micellar core and corona sizes. SDS is shown to induce partial micelle disruption together with an increase of the poly(ethylene oxide) corona extension from 25% (without SDS) to 70% (with SDS) of a completely extended PEOi u chain. Our data at the silica-water interface are compatible with the adsorption of micelles. [less ▲]

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See detailThe Photoionization Mass Spectrometric Study of the Three membered Ring Systems C3H6, C2H4O and C2H4S and their open Chain Isomers.
Locht, Robert ULg; Leyh, Bernard ULg; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H - on CD-ROM (2004)

The dissociative photoionization mass spectrometric study of C2H6, C2H4O and C2H4S has been measured using synchrotron radiation. The ionization efficiency curves of the molecular ions of the three ... [more ▼]

The dissociative photoionization mass spectrometric study of C2H6, C2H4O and C2H4S has been measured using synchrotron radiation. The ionization efficiency curves of the molecular ions of the three species are reported. [less ▲]

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See detailThe Vacuum UV Photoabsorption Spectroscopy of the Three membered Ring Systems C3H6, C2H4O and C2H4S and their open Chain Isomers.
Locht, Robert ULg; Leyh, Bernard ULg; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Elektronen Synchrotron Strahlung m.b.H - on CD-ROM (2004)

The vacuum UV photoabsorption spectrum of C3H6, C2H4O and C2H4S have been measured using synchrotron radiation and are reported.

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See detailKinetic Energy Release Distributions for Tropylium and Benzylium Ion Formation from the Toluene Cation.
Fati, D.; Lorquet, Andrée ULg; Locht, Robert ULg et al

in Journal of Physical Chemistry A (2004), 108

Hydrogen loss from the toluene molecular ion generates benzylium (Bz(+)) and tropylium (Tr+) ions via two competitive and independent pathways. The corresponding kinetic energy release distributions ... [more ▼]

Hydrogen loss from the toluene molecular ion generates benzylium (Bz(+)) and tropylium (Tr+) ions via two competitive and independent pathways. The corresponding kinetic energy release distributions (KERDs) have been determined under various conditions in the metastable time window for toluene and perdeuterated toluene and have been analyzed by the maximum entropy method (MEM). The isomeric fraction Tr+/Bz(+) is found to be equal to 0.9 +/- 0.3, in good agreement with the values obtained using photodissociation and charge exchange experiments. It is, however, in disagreement with the value 5 +/- 2 deduced by Moon, Choe, and Kim (J. Phys. Cheln. A 2000, 104, 458) from KERD measurements. The origin of the discrepancy is suggested to be the inadequacy of the orbiting transition state theory (OTST) for the calculation of KERDs in hydrogen loss reactions. For both channels, more translational energy is released in the reaction coordinate than would be expected on statistical grounds because of the presence of a barrier along the reaction path. For the Bz(+) channel, the barrier entirely results from centrifugal effects. Rotational energy is converted into translation as a result of angular momentum conservation. Deuteration is observed to reduce the importance of the rotational energy flow in the reaction coordinate. The Tr+ channel is characterized by the presence of a reverse activation energy barrier of electronic origin. The energy in excess of the dissociation asymptote can be partitioned into two components: the reverse barrier plus a nonfixed energy contribution. About 40% of the reverse barrier is converted into relative translational motion of the fragments. Here again, a lower fraction of the nonfixed energy flows into translation for the deuterated isotopomer. [less ▲]

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See detailStructure of diblock copolymers in aqueous solution in the presence of a classical surfactant
Vangeyte, Patrick; Leyh, Bernard ULg; Heinrich, M. et al

Poster (2003, May 16)

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See detailCharge exchange in tandem mass spectrometry: dissociative single electron capture by doubly-charged toluene cations
Fati, D.; Leyh, Bernard ULg

in European Journal of Mass Spectrometry (Chichester, England) (2003), 9(4), 223-235

Single electron capture by doubly-charged toluene cations upon collision with various target gases has been investigated by sector tandem mass spectrometry. Both non-dissociative and dissociative charge ... [more ▼]

Single electron capture by doubly-charged toluene cations upon collision with various target gases has been investigated by sector tandem mass spectrometry. Both non-dissociative and dissociative charge transfer reactions leading to C(7)H(7)(+) + H and to C(5)H(5)(+) + [C(2),H(3)] are detected. Seven atomic or molecular target gases have been used with ionisation energies ranging from 8.8 eV to 14 eV. The branching ratios between the different non-dissociative and dissociative exit channels have been determined as well as the translational energy release on the dissociation products. The experimental data are compared to the predictions of a two-state semi-classical theoretical model that takes into account the non-adiabatic transition responsible for the charge transfer reaction. A wide reaction window shows up but the internal energies of the C(7)H(8)(+) cations produced by single electron capture are observed to be larger than expected. We assign this effect partly to the influence of the large density of vibrational states and to the multichannel nature of the process. Excited states of the dication are also most probably involved in the charge exchange reaction. [less ▲]

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See detailHow ergodic is the fragmentation of the pyridine cation? A maximum entropy analysis
Gridelet, E.; Locht, Robert ULg; Lorquet, Andrée ULg et al

in International Journal of Mass Spectrometry (2003), 228(2-3), 389-402

The kinetic energy released to the C4H4+ and HCN fragments produced by the dissociation of the pyridine ion has been determined by a retarding field technique up to an internal energy of 4eV above the ... [more ▼]

The kinetic energy released to the C4H4+ and HCN fragments produced by the dissociation of the pyridine ion has been determined by a retarding field technique up to an internal energy of 4eV above the reaction threshold. This extends our previous study limited to the metastable domain [Int. J. Mass Spectrom. Ion Process. 185/186/187 (1999) 155]. Retarding potential curves resulting from dissociative photoionization using the He(I), Ne(I), and Ar(II) resonance lines have been analyzed by the maximum entropy method. The comparison between the experimentally measured curves and those calculated for the prior (i.e., most statistical) situation reveals the existence of dynamical constraints that prevent phase space from being fully explored. The "ergodicity index" F(E) that measures the efficiency of phase space sampling as a function of the internal energy E of the molecular ion is found to decrease steadily as a function of E and to level off at a value of about 50% when E greater than or equal to 2.5 eV At these high internal energies where phase space exploration no longer decreases, spontaneous intramolecular vibrational energy redistribution (i.e., resulting from the anharmonicity of the molecular vibrations) is thought to contribute to internal energy randomization to a limited extent only. When the lifetime is short, phase space exploration is believed to result instead from the relaxation of the electronic energy via a cascade of non-radiative transitions, which leads to a great diversity of initial conditions, and thus, contributes to statisticity. (C) 2003 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailHow ergodic is the Fragmentation of the Pyridine Cation ? A Maximum Entropy Ananlysis
Gridelet, E.; Locht, Robert ULg; Lorquet, Andrée ULg et al

in Anton, J.; Cederquist, H.; Larsson, M. (Eds.) et al 23rd International Conference on the Photonic, Electronic and Atomic Collisions: Book of Abstracts. (2003)

The experimental KER and the statistical distributions are compared by the Maximum Entropy Method. An Ergodicity Index F(E) is defined to measure the phase space sampling efficiency. This is applied to ... [more ▼]

The experimental KER and the statistical distributions are compared by the Maximum Entropy Method. An Ergodicity Index F(E) is defined to measure the phase space sampling efficiency. This is applied to the KERD of C4H4+ cation produced by the C5H5N+ -> HCN+C4H4+ fragmentation path. In this particular case the F(E) is found to decrease steadily with increasing internal energy. [less ▲]

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See detailUnimolecular Dissociation of Halogenobenzene Cations by Phase space Theory.
Gridelet, E.; Lorquet, Jean-Claude ULg; Locht, Robert ULg et al

in Anton, J.; Cedrequist, H.; Larsson, M. (Eds.) et al 23rd International Conference on Photonic, Electronic and Atomic Collisions: Book of Abstracts. (2003)

The Orbiting Transition State version of the Phase Space Theory (PST) is used to calculate the KER distributions in the dissociation channel of X (X=I,Cl,Br)-loss from C6H5X+. The results are compared to ... [more ▼]

The Orbiting Transition State version of the Phase Space Theory (PST) is used to calculate the KER distributions in the dissociation channel of X (X=I,Cl,Br)-loss from C6H5X+. The results are compared to the experimental distribution and to that obtained by PST. [less ▲]

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See detailPhotoabsorption Spectroscopy at medium Resolution. The C2HXYZ (XYZ= H, F, Cl and/or Br) Molecules.
Locht, Robert ULg; Leyh, Bernard ULg; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H - on CD-ROM (2003)

The V-UV photoabsorption spectra of 1,1-C2H2F2, C2HBrF2 and C2HClF2 have been recorded by using synchrotron radiation and are reported.

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See detailAlkali cation attachment to derivatized fullerenes studied by matrix-assisted laser desorption/ionization
Fati, D.; Leeman, V.; Vasil'ev, Y. V. et al

in Journal of the American Society for Mass Spectrometry (2002), 13(12), 1448-1458

The complexation of alkali metal ions with amphiphilic fullerene derivatives has been investigated by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry. The ... [more ▼]

The complexation of alkali metal ions with amphiphilic fullerene derivatives has been investigated by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry. The formation of analyte ions occurs via two competing mechanisms including electron transfer from matrix-derived ions and metal ion attachment. The interplay of these processes has been examined by laser fluence dependent sample activation and by variation of the target composition. The attachment of metal ions has been established as the gentler and thus more efficient route towards the formation of intact analyte ions. Investigations into the metal ion complexation have been conducted to reveal the reactivity order of the alkali metals in these reactions and to elucidate the influence of structural differences of the analytes, as well as to unravel effects caused by the anionic counter ion of the metal. The experimental data have been derived by two complementary approaches. Competing reactants were either studied simultaneously, so that the product distribution would provide direct insight into the reactivity pattern, and/or product distributions were obtained in a large variety of separate experiments and normalized for reliable comparison. It has been found that the extent to which complexation is observed follows the charge density order of the alkali metal ions. The structural features of the fullerene-attached ligands were of profound influence on the attachment of the metal ion, inducing enhanced selectivity for the complexation with less reactive metals. The metal ion attachment is reduced with the use of smaller anionic counter ions. Rationalization of these findings is provided within the framework of the mechanisms of ion formation in MALDI. [less ▲]

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See detailHigh Resolution Photoabsorption Spectroscopy of CH3Br, CH3I and their Isotopomers.
Locht, Robert ULg; Leyh, Bernard ULg; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H - sur CD-ROM (2002)

Several spectral regions in the Vacuum UV have been recorde under high resolution conditions: i.e. 8.185-8.210 eV (2e->5pa1 Rydberg transition) in CH(D)3Br and 7.300-7.325 eV in CH(D)3I (2e->6pa1 Rydberg ... [more ▼]

Several spectral regions in the Vacuum UV have been recorde under high resolution conditions: i.e. 8.185-8.210 eV (2e->5pa1 Rydberg transition) in CH(D)3Br and 7.300-7.325 eV in CH(D)3I (2e->6pa1 Rydberg transition). These spectra were recorded with 50µeV resolution. Structures separated by 100-150 µeV are observed and are shown to be isotope dependent. [less ▲]

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See detailThe Vacuum UV Photoabsorption Spectrum of Methyl Chloride (CH3Cl) and its perdeuterated Isotopomer CD3Cl. I. A Rydberg Series Analysis.
Locht, Robert ULg; Leyh, Bernard ULg; Hoxha, A. et al

in Chemical Physics (2001), 272

The vacuum UV photoabsorption spectrum of CH3Cl has been recorded between 6 and 25 eV. A large number of vibronic bands are observed. These were partly ascribed to vibrationless Rydberg transitions. In ... [more ▼]

The vacuum UV photoabsorption spectrum of CH3Cl has been recorded between 6 and 25 eV. A large number of vibronic bands are observed. These were partly ascribed to vibrationless Rydberg transitions. In the higher energy range of 12-25 eV very weak diffuse bands are mostly assigned to transitions from the 3a1, 1e and 2a1 to 3s orbitals. In the 6-12 eV photon energy range, numerous weak to strong bands are observed. The sharpness of the features is very variable over the entire spectral region. In a first step, the interpretation of the spectrum and the assignment of the Rydberg transitions is based on the simple Rydberg formula. The observed features are classified in two groups of four series, each converging to one of the two spin-orbit components of the X2E state of CH3Cl+. Rydberg series of nsa1 (delta=1.069 and 1.064), npa1 (delta= 0.68 and 0.66), npe (delta= 0.438 and 0.427) and nd (delta= -0.040 and -0.092) characters are observed. The same measurements have been made for the first time on CD3Cl in the 6-12 eV photon energy range. The same Rydberg transitions are observed. Analogous series are characterized by about the same delta values: nsa1 (delta= 1.038 and 0.968), npa1 (delta= 0.65 and 0.61), npe (delta= 0.458 and 0.462) and nd (delta= -0.004 and -0.082). Ionization energies for CD3Cl X2E3/2 at 11.320 eV and X2E1/2 at 11.346 eV are deduced. In a second step, we fitted the experimental data for the nsa1 and npa1 states to an energy expression taking into account both the exchange interaction and the spin-orbit coupling. This accounts for the progressive switching from Hund's case (a) to Hund's case (c). [less ▲]

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See detailAbout the Photoionization of Methyl Chloride. A Threshold Photoelectron Spectroscopic and Photoionization Mass Spectrometric investigation.
Locht, Robert ULg; Leyh, Bernard ULg; Hoxha, A. et al

in Chemical Physics (2001), 272

The threshold photoelectron spectroscopic (TPES) and the photoionization mass spectrometric (PIMS) study of Methyl Chloride (CH3Cl) in the 8-20 eV photon energy is presented. The interpretation and ... [more ▼]

The threshold photoelectron spectroscopic (TPES) and the photoionization mass spectrometric (PIMS) study of Methyl Chloride (CH3Cl) in the 8-20 eV photon energy is presented. The interpretation and assignments are supported by ab initio calculations. The detailed analysis of the TPES shows numerous features in the Jahn-Teller split ground X2E(2A'-2A") state of CH3Cl+ and a new continuus band peaking at 13.4 eV. These were assigned to both direct ionization and autoionizing transitions. The transitions to the A2A1 and to the B2E states undergo a large enhancement ascribed to important autoionizing contributions. Based on the present calculations, the weak to very weak signals in the 19-26 eV photon energy range were mainly assigned to 2a1-1 ionization and to double excitations described essentially by 2e-2, 4a11 and 1e-1, 2e-1, 4a11 configurations. The PIMS study allowed us to investigate in detail the ionization and dissociation of CH3Cl+ into CH2+, CH3+, CHCl+ and CH2Cl+ from threshold up to 20 eV photon energy. At the onset, the CH3+, CHCl+ and CH2Cl+ fragment ion production is correlated to the ground state of CH3Cl+ and all fragment ions have to appear through dissociative autoionization from the 2e->3p Rydberg state. This interpretation is supported by the photoabsorption spectrum (PAS) measured recently in the same photon energy range. At higher energies, beside direct dissociation of the A2A1 and B2E states of CH3Cl+ autoionization also contributes to the fragmentation in all decay channels. For CH3+ the photoion-pair process is analyzed and detailed assignments are proposed on the basis of recent PAS data. [less ▲]

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See detailMechanism of Collisional Heating in Electrospray Mass Spectrometry: Ion Trajectory Calculations
Hoxha, Antuan; Collette, Caroline ULg; De Pauw, Edwin ULg et al

in Journal of Physical Chemistry A (2001), 105

To simulate the multicollisional heating process taking place in the intermediate pressure region of an electrospray source, ion trajectory calculations have been preformed by introducing in the SIMION ... [more ▼]

To simulate the multicollisional heating process taking place in the intermediate pressure region of an electrospray source, ion trajectory calculations have been preformed by introducing in the SIMION program a subroutine for handling the collision dynamics. The simulated internal energy distributions are compared with already available experimental distributions obtained by the "survival ion yield" method. [less ▲]

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See detailThe Vacuum UV Photoabsorption spectrum of Methyl Chloride (CH3Cl) and its perdeuterated Isotopomer CD3Cl. II. A vibrational Analysis.
Locht, Robert ULg; Leyh, Bernard ULg; Hoxha, A. et al

in Chemical Physics (2001), 272

The fine structure of the vacuum UV photoabsorption spectrum of CH3Cl and CD3Cl has been analyzed in the 7.5-10.5 eV photon energy range. A large number of lines have been observed, classified and ... [more ▼]

The fine structure of the vacuum UV photoabsorption spectrum of CH3Cl and CD3Cl has been analyzed in the 7.5-10.5 eV photon energy range. A large number of lines have been observed, classified and assigned to vibrational excitation accompanying a series of Rydberg transitions. The vibronic transitions involve both Jahn-Teller distortion and spin-orbit splitting. The former effect has been evaluated by ab initio calculations showing that the 2E state (in the C3v symmetry group) splits into 2A' and 2A" states in the Cs symmetry group. The 2A' state is energetically the lowest component whereas the 2A" is found to be a transition state. The Jahn-Teller stabilisation energy and the wavenumbers associated with all vibrational modes have been calculated. Experimentally, the entire fine structure could be described by using the vibrational modes, i.e. hcomega5= 104+/-7 meV, hcomega6= 77+/-7 meV and homega=162+/-3 meV respectively, as resulting from an average over all the analyzed Rydberg states. In CD3Cl the corresponding energies are hcomega5= 81+/-4 meV, hcomega6= 66+/-5 meV and hcomega= 124+/-4 meV. These values are in good agreement with those predicted by the present ab initio calculations for the ion ground state. However, the agreement is not so good for the wavenumber omega which could be assigned to the nu3 or nu4 vibrational modes. Though some arguments favour nu4 (the CH3 umbrella mode), within the error limits on the present measurements it is formally not possible to ascribe this wavenumber to one of these two vibrations. [less ▲]

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See detailEffectuer l'état des lieux, la réactivation et la rémédiation des bases de chimie à la charnière entre l'enseignement secondaire et l'Université sur http://www.ulg.ac.be/grptrans/
Müller, Robert; Cornélis, André; Cahay, René et al

in Bulletin de l'Association Belge des Professeurs de Physique et de Chimie (2000), (144), 30-40

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See detailDissociation of Difluoroetylene Cations: an ion-neutral complex along the fluoroethylidene+ + HF reaction path.
Leyh, Bernard ULg; Lorquet, Andrée ULg; Lorquet, Jean-Claude ULg et al

in Gelpi, E. (Ed.) 15th International Mass Spectrometry Conference: Book of Abstracts (2000)

The collision activated dissociation and dissociative photoionization of 1,1- and 1,2-C2H2F2 in the HF-loss channel are investigated. The measured KER ditributions are interpreted by the opening of two ... [more ▼]

The collision activated dissociation and dissociative photoionization of 1,1- and 1,2-C2H2F2 in the HF-loss channel are investigated. The measured KER ditributions are interpreted by the opening of two competitive reaction channels leading to two C2HF+ isomers. This hypothesis is checked by ab initio calculations. [less ▲]

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See detailUnimolecular Reaction Dynamics from Kinetic Energy Release Distributions: extent of Phase Space Sampling.
Hoxha, A.; Locht, Robert ULg; Lorquet, Andrée ULg et al

in Gelpi, Ed. (Ed.) 15th International Mass Spectrometry Conference: Book of Abstracts. (2000)

The dissociative photoionization of C2H3Br+ in the Br and HBr loss channels is reported. The KER distributions are analyzed by the Maximum Entropy Method (MEM). It can be concluded that at low and high ... [more ▼]

The dissociative photoionization of C2H3Br+ in the Br and HBr loss channels is reported. The KER distributions are analyzed by the Maximum Entropy Method (MEM). It can be concluded that at low and high internal energy the dissociations are statistical. At intermediate internal energies the excess energy is not completely randomized. [less ▲]

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