Fate of reactive intermediates formed in acetaldehyde under exposure to low-energy electrons

Chemical reactions have been induced in condensed acetaldehyde by exposure to low-energy electrons as demonstrated by use of high-resolution electron energy loss (HREEL) spectroscopy and thermal desorption spectroscopy (TDS). The HREEL spectra show that the acetaldehyde film is modified significantly when the incident electron energy is increased above 10 eV. Release of CO upon exposure to electrons at an incident energy of 14 eV is observed by electronic HREEL spectra. The changes in the vibrational spectra upon exposure of the molecular film to electrons at an incident energy of 15.5 eV are analyzed in detail using reference spectra for a number of potential product molecules. TDS data reveal clearly the decomposition of acetaldehyde and formation of CO and CH4 as major products under electron exposure. The combined results also give evidence for the formation of propionaldehyde. Other less prominent products are acetone and possibly an alcoholic species. A reaction mechanism is suggested that rationalizes the formation of larger products. It involves fragmentation of the molecule releasing CO, abstraction of an H atom from an adjacent acetaldehyde by the H radical fragment, and, finally, recombination of the resulting radical with the remaining CH3 fragment.