Momentum images of continuum electrons from the molecular ionization and dissociation of H2 induced by slow He2+ ions

Cold target recoil ion momentum spectroscopy (COLTRIM) has been employed to image the momentum distributions of continuum electrons liberated in the impact of slow He2+ on He and H2. The distributions were measured for fully determined motion of the nuclei that is as a function of the impact parameter and in a well de ned scattering plane The single ionization (SI) of H2 leading to H2+ recoil ions in nondissociative states (He2+ + H+ -> He2+ + H+ + e-) and the transfer ionization (TI) of H2 leading to H2 dissociation into two free protons (He2+ H2 -> He+ + H+ + H+ + e-) were investigated. Similar measurements have been carried out for He target, the corresponding atomic two electron system, i.e. the single ionization (SI) (He2+ + He -> He+ + He2+ e- and the transfer ionization (TI) (He2+ + He -> He+ + He2+ + e-). These measurements have been exploited to understand the results obtained for H target. In comparing the continuum electron momentum distributions for H2 with that for He, a high degree of similarity is observed. In the case of transfer ionization of H2, the electron momentum distributions generated for parallel and perpendicular molecular orientations revealed no orientation dependence. The in scattering plane electron momentum distributions for the transfer ionization of H2 by He2+ and for the transfer ionization of He by He2e showed that the salient feature of these distributions for both collisions systems consists in the appearance of two groups of electrons with difeerent structures. In addition to the group of the saddle electrons forming two jets separated by a valley along the projectile axis we nd a new group of electrons moving with a velocity higher than the projectile velocity These new fast forward electrons result from a narrow range of impact parameters and appear as image saddle in the projectile frame. In contrast to the transfer ionization of He, the fast forward electrons group disappears in the in scattering plane electron momentum distribution generated for the single ionization of He. Instead of this group another new group of electrons appear These electrons exhibit an amount of backscattering These backward elec trons appear as image saddle in the target frame The structures that the saddle electrons show are owing to the quasi molecular nature of the collision process For the TI of H2, the TI of He and the SI of He, a pi-orbital shape of the electron momentum distribution is observed This indicates the importance of the rotational coupling 2-p-theta -> 2p-pi in the initial promotion of the ground state followed by further promotions to the continuum The backward electrons as well as the fast forward electrons are not discussed in the theoretical literature at all. However, a number of obvious indications of the existence of the backward and fast forward electrons could be seen in the experimental works of Abdallah et al. as well as in the theoretical calculations of Sidky et al One might speculate that electrons which are promoted on the saddle for some time during the collision could finally swing around the He+ ion in the way out of the collision, i.e. either around the projectile in the forward direction as in the TI case forming the fast forward electrons or around the recoil ion in the backward direction as in the SI case forming the backward electrons. This might be a result of the strong gradient, and hence the large acceleration of the screened He+ potential

The γ-irradiation Effect on the Optical Properties of CdTe Thin Films Deposited by Thermal Evaporation Technique

CdTe thin films of 50 nm thickness have been deposited on glass substrates by thermal vacuum evaporation technique and the γ-irradiation effect on their optical properties has been investigated. Transmittance and reflectance have been measured at normal incidence, in the visible region from 400 to 700 nm, and were used to evaluate the optical parameters and the band gap energy for CdTe thin films before and after γ-irradiation. Structure and surface morphology before and after γ-irradiation were investigated using X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) respectively. XRD pattern of the as-deposited CdTe film shows an amorphous nature. Crystalline structure was observed to improve when samples were exposed to γ-irradiation at doses from 40 – 120 kGy in the (111) plane of the cubic zinc-blende structure. SEM shows a change in the surface morphology of CdTe films as a consequence of γ-irradiation compared to as-deposited sample. The optical properties such as refractive index, extinction coefficient, dielectric constant were found to decrease with the increase of the dose of γ-irradiation. Energy band gap was found to decrease from 2.47 eV for the as-deposited down to 2.20 eV for 120 kGy (blue shift compared to bulk CdTe), that was attributed to the small thin film thickness.DOI: http://dx.doi.org/10.5755/j01.ms.24.1.17607</p

Molecular dynamics of NH3 induced by core-electron excitation

Nuclear motion in the N1s(-1)4a(1)(1) core-excited state of ammonia is investigated by studying the angular anisotropy of fragments produced in the decay of the highly excited molecule and compared with predictions from ab initio calculations. Two different fragmentation channels (H+/NH2+ and H+/NH+/H) reveal complex nuclear dynamics as the excitation photon energy is tuned through the 4a(1) resonance. The well-defined angular anisotropy of the fragments produced in the dissociation of the molecular dication species suggests a very rapid nuclear motion and the time scale of the nuclear dynamics is limited to the low fs timescale

Contribution à la réalisation d un cd-rom d ostéologie comparée des mammifères domestiques (étude trilingue des parties consacrées au chat et au cheval)

L ostéologie est une discipline illustrée. Le CD-ROM est un outil multimédia qui représente un complément intéressant aux ouvrages plus classiques. Le but de ce travail est de participer à la réalisation d un CD-ROM quadrilingue d ostéologie comparée des Mammifères domestiques. Notre contribution concerne le Chat et le Cheval, en trois langues : français, anglais et latin ainsi qu une version hispanoanglaise de ce même CD-ROM. Après avoir présenté le guide de l utilisateur de ce CD-ROM, nous exposons les objectifs et les principales étapes qui ont été nécessaires à l élaboration de cet outil. Cette partie de CD-ROM, riche de plus de 400 photographies, permet d apprendre et de contrôler ses connaissances en ostéologie de manière attrayante. Il sera apprécié de l étudiant et de l enseignant vétérinaire (ou en médecine humaine) pour sa valeur pédagogique, comme du praticien à la recherche d information dans le cadre de son exercice professionnel. Son usage peut être étendu à de nombreux autres utilisateurs.TOULOUSE3-BU Santé-Centrale (315552105) / SudocTOULOUSE-EN Vétérinaire (315552301) / SudocSudocFranceF