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

The kinetics of SmO n + ( n = 0-2) and NdO n + ( n = 0-2) with O 3 are measured using a selected-ion flow tube. Reaction of Nd + to yield NdO + + O 2 occurs rapidly, with a rate constant near the capture-controlled limit of ∼8 × 10 -10 cm 3 s -1 . NdO + reacts at ∼40% of the capture limit to yield NdO 2 + with little temperature dependence from 200 to 400 K. NdO 2 + likely reacts very slowly ( k ∼ 10 -13 cm 3 s -1 ) to yield NdO + + 2O 2 , does not react to yield NdO 3 + , and associates slowly ( k ∼ 10 -12 cm 3 s -1 ) to yield NdO 2 + (O 3 ) 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 cm 3 s -1 ) to yield SmO 2 + + O 2 , while the excited-state SmO +* reacts at the capture limit, with branching to yield Sm + + 2O 2 (Δ H r,0K = 148.7 ± 0.4 kJ mol -1 for ground-state SmO + ) approximately 60% of the time, the remainder forming SmO 2 + , which further reacts with O 3 to yield SmO + at about 1% of the collisional value.