Electron Collisions With Ammonia And Formamide In The Low- And Intermediate-energy Ranges

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)We report an investigation on electron collisions with two nitrogen-containing compounds, namely ammonia (NH3) and formamide (NH2CHO). For ammonia, both theoretical and experimental differential, integral, and momentum-transfer cross sections, as well as calculated grand-total and total absorption cross sections, are reported in the 50-500 eV incident energy range. Calculated results of various cross sections are also reported for energies below 50 eV. Experimentally, angular distributions of the scattered electrons were measured using a crossed electron beam-molecular beam geometry and then converted to absolute differential cross sections using the relative flow technique. Absolute integral and momentum-transfer cross sections for elastic e - ammonia scattering were also derived from the measured differential cross sections. For formamide, only theoretical cross sections are presented in the 1-500 eV incident energy range. A single-center-expansion technique combined with the method of Padé was used in our calculations. For both targets, our calculated cross sections are compared with the present measured data and with the theoretical and experimental data available in the literature and show generally good agreement. Moreover, for formamide, two shape resonances located at 3.5 eV and 15 eV which correspond to the continuum 2A'' and 2A' scattering symmetries, respectively, are identified. The former can be associated to the 2B1 shape resonance in formaldehyde located at around 2.5 eV, whereas the latter can be related to the 2E resonance in ammonia at about 10 eV. Such correspondence is very interesting and so supports the investigation on electron interaction with small building blocks, instead of with larger biomolecules.906CAPES; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior; FAPESP; Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Boudaïffa, B., Cloutier, P., Hunting, D., Huels, M.A., Sanche, L., (2000) Science, 287, p. 1658. , SCIEAS 0036-8075Huels, M.A., Boudaïffa, B., Cloutier, P., Hunting, D., Sanche, L., (2003) J. Am. Chem. Soc., 125, p. 4467. , JACSAT 0002-7863Sugohara, R.T., Homem, M.G.P., Sanches, I.P., De Moura, A.F., Lee, M.T., Iga, I., (2011) Phys. Rev. A, 83, p. 032708. , PLRAAN 1050-2947Lee, M.-T., De Souza, G.L.C., Machado, L.E., Brescansin, L.M., Dos Santos, A.S., Lucchese, R.R., Sugohara, R.T., Iga, I., (2012) J. Chem. 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Correlation-Polarization Effects in Electron/Positron Scattering from Acetylene: A Comparison of Computational Models

Different computational methods are employed to evaluate elastic (rotationally summed) integral and differential cross sections for low energy (below about 10 eV) positron scattering off gas-phase C$_2$H$_2$ molecules. The computations are carried out at the static and static-plus-polarization levels for describing the interaction forces and the correlation-polarization contributions are found to be an essential component for the correct description of low-energy cross section behavior. The local model potentials derived from density functional theory (DFT) and from the distributed positron model (DPM) are found to produce very high-quality agreement with existing measurements. On the other hand, the less satisfactory agreement between the R-matrix (RM) results and measured data shows the effects of the slow convergence rate of configuration-interaction (CI) expansion methods with respect to the size of the CI-expansion. To contrast the positron scattering findings, results for electron-C$_2$H$_2$ integral and differential cross sections, calculated with both a DFT model potential and the R-matrix method, are compared and analysed around the shape resonance energy region and found to produce better internal agreement

MODELS FOR HIGH ENERGY ION INDUCED DESORPTION OF MOLECULES FROM SURFACES

Des calculs classiques de trajectoires de molécules désorbées de surfaces sont considérés. Une chaîne linéaire d'oscillateurs inharmoniques est utilisée pour modéliser le système. Des résultats pour le mécanisme "popcorn" et pour la désorption thermique sont donnés. Dans les deux cas le mécanisme principal pour la désorption s'avère être le couplage du mode d'expansion du système au mode de désorption.Classical trajectory calculations of the desorption of large molecules from surfaces are considered. A linear chain of anharmonic oscillators is used to model the system. Results for the "popcorn" mechanism and for thermal desorption are given. In both cases the main mechanism for desorption is found to be the coupling of the expansion mode of the system to the desorption mode

Circular dichroism in molecular frame photoelectron emission from space fixed oriented molecules : a complete experiment with a single circular polarization of the light

International audienc

Shape and Feshbach resonances in inner-shell photodetachment of negative ions

nner-shell photodetachment of negative ions has been investigated using the photon-ion merged beam technique for atomic and small cluster systems. The case of atomic systems is illustrated by reporting on the first measurements of the absolute cross-sections for the formation of Pt(+), pt(2+), and Pt(3+) following 4f and 5p inner-shell photoexcitation and detachment of Pt(-) 4f(14)5d(9)6s(2) (2)D. The Pt(3+) production channel is dominated by 4f detachment and allows for the first observation of a d-wave Wigner threshold law following single-photon absorption. Our measurements show that promoting a 5p electron into the 5d orbital produces a shape resonance, while promoting a 4f electron produces Feshbach resonances, demonstrating the importance of core-valence interactions. The photodetachment of small cluster systems is illustrated with the measurement and the calculation of K-shell photodetachment of size-selected B(2)(-) and B(3)(-) clusters. The experimental absolute photodetachment cross-sections exhibit bound resonances below threshold and two shape resonances above the K-shell threshold. Similar results were obtained for all of the cationic products observed, B(+) and B(2)(+). from B(2)(-), as well as B(+), B(2)(+) and B(3)(+) from B(3)(-). The overall agreement between measured and calculated photodetachment cross-sections is very good. (C) 2010 Elsevier B.V. All rights reserved

Photoelectron trapping in N 2 O 7\u3c3\u2192k\u3c3 resonant ionization

Vibrationally resolved photoelectron spectroscopy of the N(2)O(+)(A (2)Sigma(+)) state is used to compare the dependence of the photoelectron dynamics on molecular geometry for two shape resonances in the same ionization channel. Spectra are acquired over the photon energy range of 18 k sigma channel and one in the 7 sigma -> k pi channel. Vibrational branching ratio curves are determined by measuring vibrationally resolved photoelectron spectra as a function of photon energy, and theoretical branching ratio curves are generated via Schwinger variational scattering calculations. In the region 30 k pi channel. This k sigma resonance is manifested in non-Franck-Condon behavior in the approximately antisymmetric nu(3) stretching mode, but it is not visible in the branching ratio curve for the approximately symmetric nu(1) stretch. The behavior of the 35-eV k sigma resonance is compared to a previously studied N(2)O 7 sigma -> k sigma shape resonance at lower energy. The mode sensitivity of the 35-eV k sigma resonance is the opposite of what was observed for the lower-energy resonance. The contrasting mode-specific behavior observed for the high- and low-energy 7 sigma -> k sigma resonances can be explained on the basis of the "approximate" symmetry of the quasibound photoelectron resonant wave function, and the contrasting behavior reflects differences in the continuum electron trapping. An examination of the geometry dependence of the photoelectron dipole matrix elements shows that the k sigma resonances have qualitatively different dependences on the individual bond lengths. The low-energy resonance is influenced only by changes in the end-to-end length of the molecule, whereas the higher-energy resonance depends on the individual N-N and N-O bond lengths. Branching ratios are determined for several vibrational levels, including the symmetry-forbidden bending mode, and all of the observed behavior is explained in the context of an independent particle, Born-Oppenheimer framework

Histomorphometric evaluation of two different bone substitutes in sinus augmentation procedures: A randomized controlled trial in humans

Purpose: The histomorphometric results of sinus floor augmentation with deproteinized bovine bone (DBB) and a new fully synthetic bone substitute, poly(lactic-co-glycolic acid/hydroxyapatite) (PLGA/HA), were compared in humans. Materials and Methods: Twelve maxillary sinuses of eight patients requiring major maxillary sinus floor augmentation and free of concomitant conditions (ASA scores 1 and 2) were studied. Lateral sinus augmentation was performed using DBB or PLGA/HA grafts; sites were randomly assigned to control or test groups. Patients were reexamined approximately 6 months after grafting using cone beam computed tomography scans, and biopsy samples were harvested from implant sites. Total bone volume, residual graft material volume, and new bone volume were assessed. Results: Healing times were similar between groups. Measurable biopsy specimens were available from four of the test sites and six of the control sites. PLGA/HA grafts showed no trace of graft material, whereas DBB grafts had a mean graft area of 16.5% (P <.05). Mean percent newly formed bone tended to be greater for PLGA/HA (44.45%) than for DBB (27.51%). Mean total volume percent did not differ significantly: PLGA/HA = 44.45%, DBB = 44.10%. Conclusion: DBB and PLGA/HA produced similar total bone volumes. PLGA/HA appeared to be completely resorbed, whereas DBB presented residual graft material. With the limitations due to the small sample size, both materials were suitable for sinus floor augmentation.Purpose: The histomorphometric results of sinus floor augmentation with deproteinized bovine bone (DBB) and a new fully synthetic bone substitute, poly(lactic-co-glycolic acid/hydroxyapatite) (PLGA/HA), were compared in humans. Materials and Methods: Twelve maxillary sinuses of eight patients requiring major maxillary sinus floor augmentation and free of concomitant conditions (ASA scores 1 and 2) were studied. Lateral sinus augmentation was performed using DBB or PLGA/HA grafts; sites were randomly assigned to control or test groups. Patients were reexamined approximately 6 months after grafting using cone beam computed tomography scans, and biopsy samples were harvested from implant sites. Total bone volume, residual graft material volume, and new bone volume were assessed. Results: Healing times were similar between groups. Measurable biopsy specimens were available from four of the test sites and six of the control sites. PLGA/HA grafts showed no trace of graft material, whereas DBB grafts had a mean graft area of 16.5% (P <.05). Mean percent newly formed bone tended to be greater for PLGA/HA (44.45%) than for DBB (27.51%). Mean total volume percent did not differ significantly: PLGA/HA = 44.45%, DBB = 44.10%. Conclusion: DBB and PLGA/HA produced similar total bone volumes. PLGA/HA appeared to be completely resorbed, whereas DBB presented residual graft material. With the limitations due to the small sample size, both materials were suitable for sinus floor augmentation

Complete description of linear molecule photoionization achieved by vector correlations using light of a single circular polarization

In this paper we demonstrate that the vector correlation approach for the study of dissociative photoionization (DPI) of linear molecules enables us to achieve a complete description of molecular photoionization by performing a single experiment using only one state of circularly, or elliptically, polarized light. This is illustrated by the derivation of the complex dipole matrix elements for the benchmark DPI reaction of the NO molecule, where (4)–1 inner-valence ionization is induced by left-handed circularly polarized synchrotron radiation at h= 23.65 eV. The importance of electronic correlation for this process is emphasized by comparing the experimental results with multichannel Schwinger configuration interaction calculations. The energy dependence of the transition matrix elements and that of the electronic correlation in the 25–40 eV energy range are illustrated by the calculations and compared with the present results and recent experimental studies at 40.8 eV