Drift tube measurements of the temperature dependence of ion association reactions in atmospheric gases

Association reactions of NO+, O2+, N+, and N2+ ions with N2 and CO2 have been studied as a function of gas temperature using a variable-temperature drift-tube mass-spectrometer apparatus. The observed variation of the forward rate coefficients with temperature (typically 100 K - 400 K) can be expressed in the form of power laws of the form k = C(T/300)sup(x), with x ranging from 2.2 to 4.3. In a second set of measurements, we have employed a selected ion drift apparatus (SIDA) to determine product ion yields for several fast reactions of H+, D+, and N+ ions with methane. It is found that the product ion yields exhibit a pronounced variation with ion energy (0.04 - 0.2 eV in the lab frame), even though the total rate coefficients are independent of energy. Generally, charge transfer branches are found to dominate over rearrangement reaction as the ion energy is increased. (Authors)