Chemi-ionization reactions of La, Pr, Tb, and Ho with atomic O and La with N2O from 200 to 450 K

Abstract

The chemi-ionization rate coefficients of La, Pr, Tb, and Ho with O have been measured from 200 to 450 K using a thermalized flow tube apparatus. Both La and Tb were found to react near the calculated hard sphere collision limit, while the Pr and Ho reactions proceeded at roughly 40% of that limit at all temperatures. The efficiencies of these reactions are considered and the near thermoneutral character of the reaction with Ho can explain this case, whereas an explanation for the inefficiency of the Pr reaction remains elusive. The chemi-ionization reaction of La with N2O was also studied and found to proceed roughly 2 orders of magnitude slower than the competing neutral oxidation pathway. The latter result disagrees with previous literature reports.