Gerardo Gerson Bezerra de Souza

Ionic desorption in PMMA-gamma-Fe2O3 hybrid materials induced by fast electrons: an experimental and theoretical investigation.

Poly(methylmetacrilate)-maghemite (PMMA-gamma-Fe2O3) hybrid material was studied by the electron stimulated ion desorption (ESID) techniques coupled with time-of-flight mass spectrometry (TOF-MS) and theoretical investigation about its fragmentation. Moreover, atomic force microscopy was utilized to characterize the morphology before and after ionic desorption. ESID results indicated differences of pattern fragmentation for different compositions of hybrid material in comparison with neat PMMA. Theoretical studies suggest that kinetics effects can take place in the fragmentation process and electrostatic contributions were important in the stabilization of PMMA on maghemite after the grafting process.

FRAGMENTAÇÃO DE MOLÉCULAS PELA LUZ SÍNCROTRON E POR ELÉTRONS RÁPIDOS. I. O CASO DO HALOTANO, C2F3HClBr

The photofragmentation of a core-excited halogenated compound, Halotane (C2F3HClBr), generally used as anesthetic by inhalation, has been studied using high energy photons and electrons near C 1s ionization edge (~ 300 eV), using time-of-flight mass spectrometry in multicoincidence mode. We observe strong differences between the molecular fragmentation induced by photons and electron impact.

New and simple mass calibration procedure for time-of-flight studies of electron stimulated desorption of ions from solid samples

A technique that provides a simple mass scale calibration for linear time-of-flight (TOF) measurements is presented. This procedure has been used in the calibration of the mass scale in experiments of electron stimulated desorption of ions from solid surfaces. It is based on the admission of one or more calibration rare gases inside the ultrahigh vacuum chamber while a TOF spectrum of desorbing ions from the surface is simultaneously recorded. Peaks related to desorbing ions as well as to the atomic gases can consequently be observed in the same mass spectrum, thus allowing an exact mass scale calibration. The present calibration procedure is especially suitable in the low mass range (<200 amu) and can be easily adapted for photon stimulated desorption experiments.

Irradiação de polímeros com feixe de elétrons: caracterização de íons positivos através da técnica de tempo-de-vôo

With the aim of studying the interaction of fast electrons with solid surfaces we have developed an experimental set-up based on electron stimulated desorption (ESD) coupled to time-of-flight (TOF) mass spectrometry. Poly(methyl methacrylate) and poly(vynil chloride) samples have been irradiated by a pulsed electron beam of 1.2 keV and 0.18 µs FWHM. The results show that H+ is the main ionic species to desorb after electron bombardment. In addition, other ionic fragments were also observed and assigned. These results show the potentiality of this technique in the study of ESD of polymers.

SBQ-25 anos: Físico ; Química

The authors present a concise but critical review on the development of physical chemistry in Brazil, as seen by two experimental scientists with more then 25 years of experience in the Brazilian academics.

Fotodegradação de polímeros clorados irradiados com a luz síncrotron - I. Emissão de gases

Chlorinated polymers (PVC, PVDC and E-CTFE) were irradiated with white light produced at the Brazilian Synchrotron Light Source (LNLS). The emitted gases were analyzed by mass spectrometry. The spectra were dominated by peaks related to hydrochloric acid, HCl, and chlorine (35Cl). The measured HCl intensity is used to evaluate the sensitivity of the polymers over a broad energy range. PVDC showed the greatest light sensitivity as compared to PVC and E-CTFE.

Photoabsorption of hydrocarbons in Titan's atmosphere

Titan, the largest satellite of the planet Saturn, has a thick atmosphere which consists of nitrogen (N 2 ) and methane (CH 4 ). In 2004, the Cassini-Huygens mission observed the occultation of two stars through the atmosphere of Titan and measured ultraviolet (UV) absorption spectra. Through these spectra it was possible to identify the molecular species contained in this environment. In the present work, we have simulated a spectrum of this atmosphere using some molecules such as CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , C 4 H 2 , and C 6 H 6 . Our cross sections data were experimentally obtained using the electron energy-loss technique, where the electron energy-loss spectra, measured high incident energies and in small scattering angles, are similar to photoabsorption spectra. The comparison of our synthetic spectrum with that measured by Cassini shows that this method is very efficient for identifying molecules as well as estimating abundances.