Kinetics of chemi-ionization reactions of lanthanide metals (Nd, Sm) from 150 to 450 K

The kinetics of chemi-ionization reactions of neodymium and samarium atoms with an oxygen atom to yield a metal monoxide cation and electron were studied using a flow tube apparatus over a temperature range of 150–450 K. Nd reacts efficiently with O, near the hard-sphere collision limit at all temperatures, with a rate constant of 3 × 10⁻¹⁰ cm³ s⁻¹ at 300 K and a slight positive temperature dependence. No chemi-ionization of Nd with N₂O was observed, despite the reaction being exothermic. Chemi-ionization of Sm with O is slow, with a rate constant at 300 K determined to be 7 × 10⁻¹² cm³ s⁻¹, although with large uncertainty. The Sm reaction also shows a slightly positive temperature dependence, described by a small activation energy of 60 meV. Although not definitive, the data suggest that excited states of Sm react efficiently whereas ground state Sm reacts inefficiently