Rate coefficients for oxidation of Ti+ and Th+ by O2 and NO at low energies

Rate coefficients have been determined in a drift tube‐mass spectrometer apparatus for the oxidation reactions of Ti+ and Th+ ions in O2 and NO for ion mean energies ranging from thermal (300 K) to 5 eV. Formation of the first oxides of metal ions M+ in the reactions M+ + O2 (NO) → MO+ + O (N) is found to occur with rate coefficients close to the theoretical maximum values (i.e., the ``Langevin'' limit), except for Ti+ + NO, which proceeds more slowly. Further oxidation in the reactions MO++O2 (NO)→ MO2++ O(N) has been detected only for M = Th and with small rate coefficients. The associative ionization reaction Th + O2→ ThO2+ + e has been observed to occur, although no rate coefficient can be obtained from our measurements. In addition, thermal energy ionic mobilities of thorium and titanium ions in helium are found to be μ0(Ti+) = (25.5±1) and μ0(Th+) = (15.75±0.5) cm2 V−1·sec−1 at 300 K.