Excitation of the methyl methacrylate molecule in the VUV range by angle-resolved EELS

Abstract

Angle-resolved electron energy loss spectra for the methyl methacrylate molecule have been measured at an impact energy of 1 keV. The spectra cover an excitation energy range of 0 to 100 eV and an angular range of 2° to 10°. Within our knowledge, this is the first gas-phase excitation spectrum for MMA in this energy range. At small angles the spectra are dominated by an intense peak at 6.7 eV followed by a broad band centered at about 16 eV. As the scattering angle increases, the intensity maximum in the spectra shifts towards higher energies. The generalized oscillator strength (GOS) for the 6.7 eV peak has been determined in the 0.090 to 1.093 au K 2 range. The absolute elastic differential cross section has also been obtained through normalization of the relative data to the theoretical value, determined by using the independent atom model (IAM) approximation. CI-level theoretical calculations have been also performed in order to assign the low-lying energy states. The experimentally determined value for the optical oscillator strength (0.18) for the 6.7 eV peak showed a good agreement with the theoretical result.