EXCITATION OF THE METHYL-METHACRYLATE MOLECULE IN THE VUV RANGE BY ANGLE-RESOLVED EELS

Angle-resolved electron energy loss spectra for the methyl methacrylat e molecule have been measured at an impact energy of 1 keV, The spectr a cover an excitation energy range of 0 to 100 eV and an angular range of 2 degrees to 10 degrees, Within our knowledge, this is the first g as-phase excitation spectrum for MMA in this energy range, At small an gles the spectra are dominated by an intense peak at 6.7 eV followed b y a broad band centered at about 16 eV, As the scattering angle increa ses, the intensity maximum in the spectra shifts towards higher energi es. 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 elast ic differential cross section has also been obtained through normaliza tion of the relative data to the theoretical value, determined by usin g the independent atom model (IAM) approximation, CI-level theoretical calculations have been also performed in order to assign the low-lyin g energy states. The experimentally determined value for the optical o scillator strength (0.18) for the 6.7 eV peak showed a good agreement with the theoretical result. (C) 1997 Published by Elsevier Science B. V.