Gas-phase reaction of daughter ions from the decay of multitritiated propane with benzene and toluene. Solution of a long-standing anomaly.

The population of the daughter ions from the decay of multitritiated propane has been sampled by using as a probe their gas-phase reactions with benzene and toluene at pressures up to 400 torr. Tritiated n- and isopropylated arenes account together for 70-75% of the total activity of the decay ions. This observation-and the failure to detect aromatic allylation-removes an early radiochemical anomaly, by showing that decay of tritiated propane yields propyl ions as the most abundant daughter species, following a trend established for all other tritiated hydrocarbons. The abnormally high abundance of allyl ions measured by mass spectrometry is traced to the decomposition C3H7-+ C3H6++ H 2a llowed by its low activation energy, the lack of collisional stabilization, and the long residence time which characterizes operation of a "charge" mass spectrometer. The excitation energy required for the decomposition is likely to arise from the deformation energy of the propyl cations, born from the sudden nuclear transition in a shape reminiscent of the parent hydrocarbon molecule.