Excitação eletrônica das moléculas de metacrilato de metila e estireno na região do ultravioleta de vácuo

Abstract

do Valonguinho-Centro-24210-140-Niterói-RJ Recebido em 7/1/97; aceito em 21/5/97 ELECTRONIC EXCITATION OF THE METHYL METHACRYLATE AND STYRENE MOLECULES IN THE VUV RANGE. Angle-resolved electron energy-loss spectra have been measured for the methyl methacrylate (MMA) and styrene molecules in the 0-50 eV energy range. The spectra have been obtained at 1 keV incident energy, with an energy resolution of 0.8 eV and covering an angular range of 2.0 to 7.0 degrees. Within our knowledge, this is the first gas-phase excitation spectrum for MMA and styrene in this energy range. The spectra of MMA at small scattering angles are dominated by an intense peak at 6.7 eV followed by a broad band centered at about 16 eV. In the case of styrene, six bands can be observed in the spectra. Based on the angular behaviour of the excitation spectra of these molecules, the low-lying peaks observed are considered to be associated predominantly with dipole-allowed processes. In both cases, new bands can be observed for excitation energies greater than 20 eV. This could be associated with dipoleforbidden transitions to shake-up and doubly-excited states.

Optical Properties and van der Waals - London Dispersion Interactions of Polystyrene Determined by Vacuum Ultraviolet Spectroscopy and Spectroscopic Ellipsometry

“…These E 3 transitions have the characteristic critical point line shapes associated with one-dimensionally delocalized electron states in the polymer backbone. The assignment of the E 1 transitions to excitations of the side chain aromatic ring of PS is also supported by recent work on styrene monomers, [26] with an observed shift of the aromatic ring transitions from 7.7 eV in the monomer to 6.3 eV in the polymer. A small shoulder at 9.9 eV (E 2 ) is associated with excitations possibly from either residual monomer or impurities.…”

“…The f-sum rule for the effective number of electrons per monomeric unit through the 6.7 eV peak gives 0.3 instead of the expected six electrons. Rocco et al [26] published the measured electronic excitations and optical transitions of styrene (S) and MMA (methyl methacrylate) monomers. For styrene monomers they found electronic transition energies at 5.3, 7.7, 10.3, 11.8, 13.7, and 17.1 eV.…”