Fragmentation of the Excited Parent Ions, [CH3Kr82]+ and [CH3O18]—, Following the β— Decay of CH3Br82 and the β+ Decay of CH3F18

The relative abundances of the fragment ions that result, respectively, from the β— decay of CH3Br82 and β+ decay of CH3F18 have been measured with a specially designed mass spectrometer. Following the β— decay of CH3Br82, only about 0.4% of the parent ion, CH3Kr+, remained intact, as was anticipated from the rather large recoil energy. The most abundant ion observed was CH3+, 89%. A variety of other ions were also formed and their production is discussed in terms of excitation resulting from a sudden change in nuclear charge. The investigation of the fragment ions formed in the decay of CH3F18 marks the first time a molecule undergoing positron decay has been so studied. The following negative ions were detected: CH3O—, O—, and H—. A large abundance of positive ions, however, was also observed. The origin of these positive ions is critically discussed; and calculations of the probabilities for electron shakeoff following both positron and negatron decay are given for several atomic systems.