Chemisorption of H2 on W(100): Absolute sticking probability,coverage, and electron stimulated desorption |
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Authors: | Theodore E Madey |
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Institution: | National Bureau of Standards, Washington, D.C. 20234, U.S.A. |
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Abstract: | Measurements of both the absolute sticking probability near normal incidence and the coverage of H2 adsorbed on W(100) at ~ 300K have been made using a precision gas dosing system; a known fraction of the molecules entering the vacuum chamber struck the sample crystal before reaching a mass spectrometer detector. The initial sticking probability S0 for H2/W(100) is 0.51 ± 0.03; the hydrogen coverage extrapolated to S = 0 is 2.0 × 1015 atoms cm?2. The initial sticking probability S0 for D2/W(100) is 0.57 ± 0.03; the isotope effect for sticking probability is smaller than previously reported. Electron stimulated desorption (ESD) studies reveal that the low coverage β2 hydrogen state on W(100) yields H+ ions upon bombardment by 100 eV electrons; the ion desorption cross section is ~ 1.8 × 10?23 cm2. The H+ ion cross section at saturation hydrogen coverage when the β1 state is fully populated is ? 10?25 cm2. An isotope effect in electron stimulated desorption of H+ and D+ has been found. The H+ ion yield is ? 100 × greater than the D+ ion yield, in agreement with theory. |
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