Production, characterization and scattering of a sulfur atom beam: Interatomic potentials for the rare-gas sulfides, RS (R = Ne, Ar, Kr, Xe)

Abstract

An intense and stable continuous beam of S atoms and SO radicals is produced from a microwave discharge source operating in a SO₂–He mixture. The S-atom beam, characterized by coupling mechanical velocity selection with magnetic analysis and detected by a quadrupole mass filter, has been employed in scattering experiments. The transmittance across a Stern–Gerlach magnetic selector, measured mass-spectrometrically at m/z=32 and 34 as a function of the beam velocity and of the deflecting field strength, indicates that the sulfur atoms are mainly in their electronic ground state ³P_j, with fine structure levels j=0, 1, 2 populated according to their degeneracies. Total integral cross-sections for collisions of S (³P_j) atoms with Ne, Ar, Kr and Xe have been measured in the beam velocity range 1.0–2.4 km s⁻¹. The scattering data exhibit a glory interference effect with quenching of the amplitude of the glory pattern which increases along the rare-gas series from Ne to Xe. The results are analysed to yield a characterization of the spherical and anisotropic components of the interaction, providing lengths and strengths of the bonds in the six low lying states of the rare-gas sulfides NeS, ArS, KrS and XeS.