Gas-Phase Reactivity of Ozone with Lanthanide Ions (Sm⁺, Nd⁺) and Their Higher Oxides

The kinetics of SmO⁺ (n = 0-2) and NdO⁺ (n = 0-2) with O₃ are measured using a selected-ion flow tube. Reaction of Nd⁺ to yield NdO⁺ + O₂ occurs rapidly, with a rate constant near the capture-controlled limit of ∼8 × 10^-10 cm³ s^-1. NdO⁺ reacts at ∼40% of the capture limit to yield NdO₂⁺ with little temperature dependence from 200 to 400 K. NdO₂⁺ likely reacts very slowly (k ∼ 10^-13 cm³ s^-1) to yield NdO⁺ + 2O₂, does not react to yield NdO₃⁺, and associates slowly (k ∼ 10^-12 cm³ s^-1) to yield NdO₂⁺(O₃)_1-3. Reaction of Sm⁺ also yields SmO⁺ at near the capture limit at all temperatures, but a significant fraction (∼50%) of the SmO⁺ is produced in excited states that are long-lived compared to the millisecond time scale of the experiment. These states are evidently resistant to both radiative and collisional relaxation. The excited-state production is likely due to a spin-conservation constraint on the reaction, despite the large spin-orbit coupling typical for lanthanide-containing species. Ground-state SmO⁺ reacts inefficiently (k = 2 × 10^-11 (T/300)^-2.5 cm³ s^-1) to yield SmO₂⁺ + O₂, while the excited-state SmO^+* reacts at the capture limit, with branching to yield Sm⁺ + 2O₂ (ΔH_r,0K = 148.7 ± 0.4 kJ mol^-1 for ground-state SmO⁺) approximately 60% of the time, the remainder forming SmO₂⁺, which further reacts with O₃ to yield SmO⁺ at about 1% of the collisional value.