Parcourir Sciences Et Techniques thématique/sous thématique "Physique, chimie, mathématiques & sciences de la terre"
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Electron-impact ionization and dissociation of C2D+
2010, HENALLUXArticle scientifiqueAbsolute cross sections for electron-impact single ionization, dissociative excitation and dissociative ionization of the ethynyl radical ion (C2D+) have been measured for electron energies ranging from the corresponding reaction thresholds to 2.5 keV. The animated crossed electron-ion beam experiment is used and results have been obtained for the production of C2D2+, C2+, C+2, CD+, C+ and D+. The ... -
Electron-impact ionization of atomic hydrogen: dynamical variational treatment
2011, HENALLUXArticle scientifiqueA simple and straightforward calculating scheme is proposed for electron-impact single and multiple ionization of atoms. The method is based on the application of the Hulthén-Kohn dynamical variational principle. An effective charge seen by the scattered electron is determined for a certain type of trial wave functions mathematically in a rigorous way excluding any empirical assumptions. Validity ... -
Electron-impact ionization of singly-charged neon ions
2008, HENALLUXArticle scientifiqueAbsolute cross sections for electron-impact single and multiple ionization of Ne+ leading to the formation of Neq+ (q = 2–5) are reported. The animated crossed beams method is applied in the energy range from the respective thresholds up to 2.5 keV. The maximum cross sections are found to be (4.12 ± 0.21) × 10−17 cm2, (1.42 ± 0.07) × 1018 cm2, (2.57 ± 0.14) × 10−20 cm2, (8.78 ± 0.54) × 10−22 cm2 for ... -
Energy distributions of H+ fragments ejected by fast proton and electron projectiles in collision with H2O molecules
2009, HENALLUXArticle scientifiqueExperimental measurements of the kinetic energy distribution spectra of H + fragment ions released during radiolysis of water molecules in collision with 20, 50, and 100 keV proton projectiles and 35, 200, 400, and 1000 eV electron projectiles are reported using a pulsed beam and drift tube time-of-flight based velocity measuring technique. The spectra show that H + fragments carrying a ... -
I. Electron-impact ionization and dissociation of C2H +2 and C2D +2
2010, HENALLUXArticle scientifiqueAbsolute cross-sections for electron-impact ionization and dissociation of C2H +2 and C2D +2 have been measured for electron energies ranging from the corresponding thresholds up to 2.5 keV. The animated crossed beams experiment has been used. Light as well as heavy fragment ions that are produced from the ionization and the dissociation of the target have been detected for the first time. The maximum ... -
II. Electron-impact dissociative excitation of C2H +2 and C2D +2
2010, HENALLUXArticle scientifiqueAbsolute cross-sections for electron-impact dissociative excitation of C2H +2 and C2D +2 to C2D+, CH+, C+, C +2, H+ and CH +2 singly-charged fragments have been estimated. The animated crossed-beams method is applied in the energy range from the corresponding reaction threshold up to 2.5 keV. Individual contributions for dissociative excitation are determined from the analysis of the total absolute ... -
III. Electron-impact dissociative ionization of C2H +2 and C2D +2
2010, HENALLUXArticle scientifiqueAbsolute cross-sections for electron-impact dissociative ionization of C2 H +2 and C2 D +2 to CH+, C+, C +2 , H+, CH +2 and C2D+ fragments are determined for electron energies ranging from the corresponding threshold to 2.5 keV. Results obtained in a crossed beams experiment are analyzed to estimate the contribution of dissociative ionization to each fragment formation. The dissociative ionization ... -
Isotope effects in electron-impact dissociation of D2H+
2011, HENALLUXArticle scientifiqueAbsolute cross sections have been measured using the crossed electron–ion beams method for electron-impact dissociation of the D2H+ molecular ion yielding H+, D+, HD+ and D+2 fragments. The collision energy ranges from a few eV up to 2.5 keV. Around the maximum, cross sections are found to be of a similar amplitude: (3.25 ± 0.08) × 10−17 cm2 for H+, (3.56 ± 0.15) × 10−17 cm2 for HD+ and (3.33 ± 0.11) ... -
Mass Spectrometric Investigation of Anions Formed upon Free Electron Attachment to Nucleobase Molecules and Clusters Embedded in Superfluid Helium Droplets
2006, HENALLUXArticle scientifiqueHere we report the first mass spectrometric study of negative ions formed via free electron attachment (EA) to nucleobases (NBs) embedded in helium clusters. Pure and mixed clusters of adenine and thymine have been formed by pickup of isolated NB molecules by cold helium droplets. In contrast to EA of isolated molecules in the gas phase we observe a long-lived parent anion NB− and, in addition, ... -
Multiple ionization of C+, N+ and O+ ions by fast electron impact
2013, HENALLUXArticle scientifiqueAbsolute cross sections for electron impact single and multiple ionization of C+, N+ and O+ ions leading to the formation of Cq + (q = 2–4), Nq + (q = 2–5) and Oq + (q = 2–5) are reported. The animated crossed beam method is applied in the energy range extending from the respective thresholds up to 2.5 keV. The concerned target ions belong to the second row of the periodic table, with configurations ... -
Nuclear spin conversion in the gaseous phase in the presence of a static electric field: Intramolecular magnetic interactions and the role of collisions
2004, HENALLUXArticle scientifiqueWhen a gaseous sample of 13CH3F is prepared with a spin-isomer population ratio (ortho and para forms) far from the equilibrium given by nuclear spin statistics, it relaxes towards this equilibrium with an exponential decay rate. This phenomenon, called nuclear spin conversion, is mainly governed by intramolecular spin-spin and spin-rotation interactions which couple two pairs of quasidegenerate ... -
Rotational dependence of the dipole moment of 13CH3F
2004, HENALLUXArticle scientifiqueWhen a gas sample of 13CH3F is prepared with a population of spin isomers far from the equilibrium given by nuclear spin statistics, it relaxes towards this equilibrium with an exponential decay rate. This rate is increased by submitting the molecules to a static electric field, emphasizing the role of the magnetic intramolecular interactions and of the collisions in the “quantum relaxation” process ... -
Rovibrational analysis of the XUV photodissociation of HeH + ions
2011, HENALLUXArticle scientifiqueWe investigate the dynamics of the photodissociation of the helium hydride ion HeH+ by XUV radiation with the aim to establish a detailed comparison with a recent experimental work carried out at the FLASH free electron laser using both vibrationally hot and cold ions. We determine the corresponding rovibrational distributions using a dissociative charge transfer setup and the same source conditions ... -
Screening effects and total cross sections of single, double and triple ionization of neon by fast electrons
2008, HENALLUXArticle scientifiqueThe Bethe–Born theory is applied to estimate the effective charges experienced by the ejected electrons at single, double and triple ionization of neon by fast electrons. The expansion coefficients appearing in the asymptotic expressions for total cross sections σn+ ~ [an+ln(Ei/In+) + bn+]/Ei are determined by fitting to these expressions the experimental data for single and multiple ionization of ... -
Spectroscopy and dynamics of the 7,7,8,8-tetracyanoquinodimethaneradical anion
2010, HENALLUXArticle scientifiqueThe photoelectron spectrum of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anion has been measured at 3.1 eV. Additionally, the ultrafast relaxation dynamics of the first excited state (12B3u) of TCNQ have been studied using time-resolved photoelectron spectroscopy, which reveals that it undergoes internal conversion back to the ground state (2B2g) with an associated lifetime of 650 fs ... -
Toward real-time charged-particle image reconstruction using polar onion-peeling
2009, HENALLUXArticle scientifiqueA method to reconstruct full three-dimensional photofragment distributions from their two-dimensional (2D) projection onto a detection plane is presented, for processes in which the expanding Newton sphere has cylindrical symmetry around an axis parallel to the projection plane. The method is based on: (1) onion-peeling in polar coordinates [Zhao et al., Rev. Sci. Instrum. 73, 3044 (2002)] in which ... -
Ultrafast Relaxation Dynamics Observed Through Time-Resolved Photoelectron Angular Distributions
2010, HENALLUXArticle scientifiqueTime-resolved photoelectron imaging of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anion is presented. Photoelectron angular distributions (PADs) are qualitatively analyzed in terms of the simple s-p model that is based on symmetry arguments. The internal conversion dynamics from the first excited state (12B3u) to the ground state (2B2g) may be observed through temporal changes in the PADs ... -
Velocity-map imaging at low extraction fields
2012, HENALLUXArticle scientifiqueWe present a velocity-map imaging (VMI) setup for photoelectron imaging that utilizes low electric extraction fields. This avoids any complications that could arise from electrostatic interactions between the extraction field and the molecular properties that are probed and has a minimal effect on the trajectory of ions in ion beam experiments. By using an attractive potential supplied to the detector, ... -
Water Fragmentation and Energy Loss by Carbon Ions at the Distal Region of the Bragg Peak
2007, HENALLUXArticle scientifiqueTime-of-flight mass spectrometry was used to investigate fragmentation and energy transfer processes in water by C ions at the distal part of the Bragg peak. Measurements of the positive ion fragments from ionization, electron capture, electron loss, transfer-loss and loss-ionization channels have allowed us for the first time (a) to obtain a quantitative determination of the energy lost by C ions ... -
Water-molecule dissociation by proton and hydrogen impact
2007, HENALLUXArticle scientifiqueTime-of-flight-based mass analysis of charged water fragments have been used to measure the dissociative and the nondissociative reaction pathways of water formed during collisions with 15 to 100 keV and 500 to 3500 keV H+ projectiles and with 8 to 100 keV H0 projectiles. The fragmentation pathways resulting from the ionization and the electron capture collisions with the incident H+ and H0 ...