Molecular beam experiments on the sticking and accommodation of molecular hydrogen on a low-temperature substrate

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Abstract
Molecular beams, microcalorimetry, and mass spectrometry are used to study the physisorption kinetics of H2 and D2 molecules on a low temperature substrate. The energy transferred to the surface of a liquid‐helium cooled bolometer by an incident room temperature beam of H2 and D2, and the number density of the scattered molecules are measured. The sticking coefficient S and the accommodation coefficient α are obtained as a function of N, the surface coverage by H2 or D2. For both isotopes, S and α depend strongly on N. S(H2) changes from 0.07±0.05 to 0.80±0.02 and α(H2) from 0.31±0.07 to 0.97±0.01 as N increases from ?0 to 3×1015 molecule cm−2. In the same coverage range, S(D2) changes from 0.25±0.05 to 0.92±0.04 and α(D2) from 0.3±0.1 to 0.975±0.025.