Ion–Molecule Reactions in Alpha-Particle Irradiated NH3, CD4, and D2O

We have investigated the time evolution of the various primary and secondary positive ion species formed in NH3, CD4, and D2O gases bombarded by 1- to 3.5-MeV alpha particles. The measurements were made with a pulsed time-of-flight mass spectrometer at pressures in the 10–40 micron range. Ion–molecule reaction schemes are proposed, the data analyzed for self-consistency, and a variety of reaction rates deduced. Comparisons are made with other experiments in which electron bombardment was used for primary ionization. Our results indicate the existence of a relatively long-lived [τ = 0.28(4)μsec] (C2D7+)* ion complex formed from the reaction CD3++CD4, paralleling previous results [R. A. Fluegge, J. Chem. Phys. 50, 4373 (1969)] for the CH4 system.