Isothermal desorption of hydrogen molecules from a W(110) surface at temperature ∼5 K

Isothermal desorption of hydrogen molecules from a W(110) surface atT _s ～ 5 K upon rapid shuttering of the molecular beam is observed in a “black chamber” type of ultrahigh-vacuum apparatus. Desorption was detected from three different states, identified as a multilayer condensation state and physisorbed states in the form of a two-dimensional gas and a two-dimensional condensate. The distribution of the physisorbed molecules between these states depends on the intensity of the flux of molecules on the surface; this appears to be responsible for the anomalous decrease of the number of isothermally desorbed molecules as the flux increases.