Formation of positive and negative ions on rhenium, oxygenated tungsten, hafnium, lanthanum hexaboride, and thoriated tungsten surfaces

Yields are reported for the formation of positive and negative ions from molecular beams striking various surfaces. Negative ions are formed from beams of several halogen compounds and tetracynoethylene on Re, Hf, thoriated W, and LaB₆ with efficiencies ranging up to a maximum of 2.6 10^-2 for KClon thoriated W (activated). This filament may be useful in detectors for some molecular-beam studies. The efficiencies for the formation of positive ions from K and potassium halides are generally in agreement with the SahaLangmuir model. They are near unity on oxygenated W, Re, and thoriated W (deactivated by heating to deplete the thorium) but much lower (2.5-6.6×10^-3) on thoriated tungsten (activated).