Estudo da excitação eletrônica de um produto natural Volátil (isopreno) por espectroscopia de impacto de elétrons na região do ultravioleta de vácuo

Abstract

The absolute values of the photoabsorption cross section of compounds are of great importance in the fields of physics, chemistry, biology, therapy and related fields. Studies of natural products are also of great importance several areas of science and innovation, however, information related to the values of the photoabsorption cross section in the vacuum ultraviolet region are scarce in the literature. In this paper a study of the electronic excitations of the molecule isoprene using a spectrometer energy loss of electrons from low-resolution (0,8– 1,0 eV FWHM) at the Laboratory for Photon and Electron Impact (LIFE-UFRJ). The energy loss spectra of electrons were obtained in the range 3-100 eV at various angles of scattering with incident energy of 1 keV. The spectra of generalized oscillator strength (GOS) for the isoprene molecule were obtained by the Bethe-Born conversion. The spectrum GOS obtained in the angle of impact 2o was extrapolated to the strength oscillator photoabsorption optical using the universal formula Msezane and Sakmar (1997). The photoabsorption cross sections on an absolute scale were determined by of the static polarizability of isoprene applying the sum rule S(-2) in the photoabsorption spectrum. The contributions of the inner layer photoabsorption above 100 eV were estimated from a fit polynomial curve. Other sum rules were used to estimate the values of physical properties isoprene as sum rule S(0) is equal to the number of electrons on the target (36,45 a. u.), the rule logarithmic L(0) is the stopping power of the molecule (18,05 a.u.), the rule logarithmic L(1) is related to the effect straggling referring to fluctuations of the incident beam (22,49 a.u.) and rule logarithmic L(2) for the Lamb shift (55,27 a.u.). The set of spectra GOS obtained at different scattering angles were presented in Bethe surface to isoprene. Two regions stand out: a region dominated by the optical selection rules for electronic transitions of the absorption, and the other region, we observed a strong angular dependence on the momentum of the incident electrons becomes significant.The Bethe surface and the sum rules are unpublished experimental data in the literature. The absolute values of the cross section and the Bethe surface can contribute to a complete understanding of the electronic excitations of the molecule isoprene induced by collisions of charged particles. It is expected that these absolute valuesmay be useful as references to theoretical calculations and experimental in the electronic spectra of isoprene.