Hyperthermal Surface Ionization

Abstract Surface ionization of molecules with hyperthermal kinetic energy (1–20 eV) was found to be very efficient, demonstrating several unique features. We have used the technique of aerodynamic acceleration in supersonic seeded beams in order to obtain molecular kinetic energies in the range 1–20 eV. Three types of hyperthermal surface ionization (HSI) processes were observed: (a) surface‐molecule electron transfer was demonstrated in the I 2 /diamond system where negative molecular iodine (I − 2 ) ions were produced; (b) molecule‐surface electron transfer was found for the anthracene molecule where positive molecular anthracene ions were generated; (c) hyperthermal surface‐induced dissociative ionization (HSIDI) was observed in 1‐iodopropane, 1‐chloro‐3‐iodopropane, benzyl bromide, and many other molecules. In these processes, we have observed a large current of negative halogen ions and positive molecular residue ions (ion‐pair formation). The mechanism of HSI is described in terms of electron transfer processes. It occurs due to a curve crossing between the neutral scattering interaction potential surface and the ionic interaction potential surface and nonunity reneutralization second curve crossing of the scattered molecules or fragment ions.

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