Chemi-ionization in collisions of metastable argon with sodium

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Abstract
Absolute and relative cross sections were obtained for the Penning-ionization (PI) reaction Ar*+Na→Ar+Na++e and the associative-ionization (AI) reaction Ar*+Na→ArNa++e. The studies were made by a merging-beams technique for a relative kinetic energy W of the reactants from nominally 0.01 to 10 eV for PI and 0.01 to 0.4 eV for AI. The Ar* represents a composite of Ar(4s 3P2) and Ar(4s 3P0). The PI is directed and occurs predominantly when the difference between the relative kinetic energy of the heavy products and the reactants is approximately 0.1 eV. Cross sections for AI are roughly proportional to W−1. Cross sections for total ionization (AI plus PI) vary as W−1/3 for the lower W.