Reactions of O− with N2, N2O, SO2, NH3, CH4, and C2H4 and C2H2− with O2 from 300 °K to relative kinetic energies of ∼2 eV

The energy dependences of the reaction rate constants of O− ions with the neutral species N2, N2O, SO2, NH3, CH4, and C2H4 have been measured from thermal energy to approximately 2 eV relative kinetic energy. The energy dependences of the over-all reaction rate constants do not fit available theories for collision rate constants. The reaction of O− with C2H4 produces four different negative-ion product channels, in addition to the associative-detachment channel. The branching ratios are found to change drastically with reactant energy. The reactions establish the following upper limits on electron affinities: EA(:C=CH2) 0.43 eV and EA(C2H3) ≳0.4 eV. The reactions also establish an upper limit for the heat of formation of the ion C2H3O− (ΔHf°−0.62 eV).