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

Abstract

The kinetics of SmO n + (n = 0–2) and NdO n + (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.

Kinetics of O3 with Ca+ and Its Higher Oxides CaOn+ (n = 1–3) and Updates to a Model of Meteoric Calcium in the Mesosphere and Lower Thermosphere

“…Experiments were conducted using the immediate output of the ozone generator (i.e., a mixture of O 2 and O 3 ), as described previously. 13 No clustering with O 2 was observed for any species, and no exothermic bimolecular reactions with O 2 were identified for any ionic species observed. The O 3 concentration was determined by monitoring the absorption through an optical cell of 7.3 cm path length at either 248 or 290 nm using a UV spectrometer (STS-UV, Ocean Insight) with a deuterium/halogen light source (DH-mini, Ocean Insight).…”

“…We note that this suggests a catalytic cycle of ozone destruction (either Ca + + 2O 3 → Ca + + 6O 2 or CaO 2 + + 2O 3 → CaO 2 + + 6O 2 ); however, because the polyatomic CaO n + species have a short lifetime to reaction with oxygen atoms, 42 this should not be a major source of O 3 destruction. We have suggested previously for the reactions 13 of NdO 2 + + O 3 and SmO 2 + + O 3 that a mechanism best described as a direct oxidation of O 3 could be occurring. This reaction is analogous to those as the termination step of the MO n + + O 3 cycle.…”

“…Reaction is the oxidation of MO n + by ozone, but reaction is equivalent to an oxidation of ozone by MO + . We have previously discussed this mechanism in the reactions of Fe + , Ni + , Sm + , and Nd + with ozone. ,, We have suggested that reaction can be described as normalM normalO n + + normalO 3 → normalM normalO n + ( O 3 ) * normalM normalO n + ( O 3 ) * → normalM normalO n + 1 + false* + normalO 2 normalM normalO n + 1 + false* → normalM normalO n − 1 + + normalO 2 → normalM normalO n + 1 …”

“…We have previously discussed this mechanism in the reactions of Fe + , Ni + , Sm + , and Nd + with ozone. 10,12,13 We have suggested that reaction 3b can be described as…”

“…Reaction is the oxidation of MO n + by ozone, but reaction is equivalent to an oxidation of ozone by MO + . We have previously discussed this mechanism in the reactions of Fe + , Ni + , Sm + , and Nd + with ozone. ,, We have suggested that reaction can be described as …”