High resolution, inelastic electron scattering data can provide new spectroscopic information on the electronic structure of polyatomic molecules. Features in the acetone energy loss spectrum from 0 to 15 eV obtained for 100 eV incident electrons correspond to vibrational, electronic discrete, and electronic continuum excitations. These data are compared with optical measurements in a wide spectral region extending from the infrared to the vacuum ultraviolet. A comprehensive interpretation of the energy loss spectra is attempted with the use of photochemical and photoelectron data, as well as quantum-chemical calculations in the literature. Three Rydberg series with quantum defects of 1.03, 0.81, and 0.315 join onto bands previously discussed in terms of transitions to valence orbitals. These series converge to an ionization limit of 9.705 eV in good agreement with previous optical determinations. Dissociative continua underlie the Rydberg region and give rise to a variety of neutral products observed in recent photolysis work. Broad features in the ionization continuum appear to correlate generally with higher ionization potentials observed by photoelectron spectroscopy. Apparent oscillator strengths derived from the energy loss data for the bands at 4.4 and 6.35 eV and for a region (9.7-11.78 eV) of the ionization continuum agree very well with the photoabsorption measurements. Integrated oscillator strengths of 0.46 below 9.7 eV and 3.93 below 15 eV were derived from the electron impact data.
Citation: Journal of Chemical Physics
Pub Type: Journals