F. Ferreira da Silva

Bio: F. Ferreira da Silva is an academic researcher from Universidade Nova de Lisboa. The author has contributed to research in topics: Electron transfer & Ion. The author has an hindex of 21, co-authored 117 publications receiving 1341 citations. Previous affiliations of F. Ferreira da Silva include University of Innsbruck & King's College London.

Modelling low energy electron and positron tracks in biologically relevant media

Abstract: This colloquium describes an approach to incorporate into radiation damage models the effect of low and intermediate energy (0-100 eV) electrons and positrons, slowing down in biologically relevant ma- terials (water and representative biomolecules). The core of the modelling procedure is a C++ computing programme named "Low Energy Particle Track Simulation (LEPTS)", which is compatible with available general purpose Monte Carlo packages. Input parameters are carefully selected from theoretical and ex- perimental cross section data and energy loss distribution functions. Data sources used for this purpose are reviewed showing examples of electron and positron cross section and energy loss data for interactions with different media of increasing complexity: atoms, molecules, clusters and condense matter. Finally, we show how such a model can be used to develop an effective dosimetric tool at the molecular level (i.e. nanodosimetry). Recent experimental developments to study the fragmentation induced in biologically material by charge transfer from neutrals and negative ions are also included.

The VUV electronic spectroscopy of acetone studied by synchrotron radiation

Abstract: The electronic state spectroscopy of acetone (CH3)2CO has been investigated using high-resolution VUV photoabsorption spectroscopy in the energy range 3.7–10.8 eV. New vibronic structure has been observed, notably in the low energy absorption band assigned to the 11A1 → 11A2 (ny → π*) transition. The local absorption maximum at 7.85 eV has been tentatively attributed to the 41A1 (π → π*) transition. Six Rydberg series converging to the lowest ionisation energy (9.708 eV) have been assigned as well as a newly-resolved ns Rydberg series converging to the first ionic excited state (12.590 eV). Rydberg orbitals of each series have been classified according to the magnitude of the quantum defect (δ) and are extended to higher quantum numbers than in the previous analyses.

The Effect of Solvation on Electron Attachment to Pure and Hydrated Pyrimidine Clusters

Abstract: The interaction of low‐energy electrons with biomolecules plays an important role in the radiation‐induced alteration of biological tissue at the molecular level. At electron energies below 15 eV, dissociative electron attachment is one of the most important processes in terms of the chemical transformation of molecules. So far, a common approach to study processes at the molecular level has been to carry out investigations with single biomolecular building blocks like pyrimidine as model molecules. Electron attachment to single pyrimidine, as well as to pure clusters and hydrated clusters, was investigated in this study. In striking contrast to the situation with isolated molecules and hydrated clusters, where no anionic monomer is detectable, we were able to observe the molecular anion for the pure clusters. Furthermore, there is evidence that solvation effectively prevents the ring fragmentation of pyrimidine after electron capture.

Selective Bond Cleavage in Potassium Collisions with Pyrimidine Bases of DNA

Abstract: We also acknowledge partial funding from the Portuguese research Grant No. PEst-OE/FIS/UI0068/2011 through FCT-MEC, and from the Spanish Ministerio de Economia y Competitividad (Project No. FIS 2009-10245). Some of this work forms part of the EU/ESF COST Actions Nano-IBCT-MP1002 and The Chemical Cosmos-CM0805

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Single Molecule Dissociation by Tunneling Electrons

Abstract: The tunneling current from a scanning tunneling microscope was used to image and dissociate single O{sub 2} molecules on the Pt(111) surface in the temperature range of 40 to 150K. After dissociation, the two oxygen atoms are found one to three lattice constants apart. The dissociation rate as a function of current was found to vary as I{sup 0.8{plus_minus}0.2} , I{sup 1.8{plus_minus}0.2} , and I{sup 2.9{plus_minus}0.3} for sample biases of 0.4, 0.3, and 0.2V, respectively. These rates are explained using a general model for dissociation induced by intramolecular vibrational excitations via resonant inelastic electron tunneling. {copyright} {ital 1997} {ital The American Physical Society}