Collision Reactions of Electronically Excited Hydrogen Molecules

Relative abundances of ions produced in collisions of metastable H2, HD, and D2 molecules with various ground-state molecules (M, RH2) are reported. It is found that, in addition to Penning ionization and fragmentation of the target ion, deuteron addition reactions D2*+M→MD++D, exchange reactions D2*+RH2→(RD2++H2), (RHD++HD), and addition reactions with exchange D2*+RH2→(RH2D++D), (RD2H++H) occur. In the case of acetylene, propyne, and the 1-alkenes C2H4, C2H6, C4H8, C6H12, the reactions are explained in terms of an intermediate ion complex RH2D2+ which decomposes within 10−6 sec. In the case of NH3 and H2O only deuteron addition without exchange occurs. This is explained in terms of a stripping mechanism. From the occurance of deuteron addition reactions in collisions with O2, H2O, HCl, CO2, and CO, a lower bound for the proton affinity of these molecules of PA ≧ 6.2 was derived.