Fragment Ions from CH3CHO and (CH3)2CO by Electron Impact

The ionization-efficiency curves for the parent and fragment ions from CH3CHO and (CH3)2CO have been examined by the second differential method. The appearance potentials for CH3CO+, namely, 10.2±0.1 eV [(CH3)2CO] and 10.5±0.2 eV (CH3CHO), are much lower than previously accepted electron-impact values. Apart from CO+(CH3CHO) no appearance potentials can be easily obtained for any of the other fragment ions. No kinetic energy was found for the light ion CH3+, nor the heavier ions CO+, HCO+(CH3CHO), and CH3CO+[(CH3)2CO].