Chemi-ionization in collisions of metastable argon with metastable krypton

Absolute and relative cross sections were obtained for the associative-ionization (AI) reaction Ar*+Kr*→ArKr++e and the Penning-ionization (PI) reactions Ar*+Kr*→Ar+Kr++e and Ar*+Kr*→Ar++Kr+e. The studies were made by a merging-beams technique for a relative kinetic energy W of the reactants from nominally 0.01 to 2 eV for AI and 0.01 to 10 eV for PI. The Ar* represents a composite of Ar(4s 3P2) and Ar(4s 3P0), and Kr* a composite of Kr(5s 3P2) and Kr(5s 3P0). The Ar*–Kr* system is moderately attractive with a well depth of a few tenths of an electron volt. The PI reactions are directed with most of the Penning ions scattered in the c.m. system in the direction of their parent reactants. The fraction of AI to total ionization (AI plus PI) is only a few percent or less. Cross sections for total ionization QT vary as W−0.40. At W=0.033 eV, QT=308×10−16 cm2. Such a relatively large QT has also been observed in this laboratory for collisions between two metastable He atoms and between metastable He and metastable Ne.