ISOTHERMAL DESORPTION OF HYDROGEN MOLECULES FROM A W(110) SURFACE AT TEMPERATURE SIMILAR-TO-5 K

Isothermal desorption of hydrogen molecules from a W(110) surface at T (s)similar to 5 K upon rapid shuttering of the molecular beam is obser ved in a ''black chamber'' type of ultrahigh-vacuum apparatus. Desorpt ion was detected from three different states, identified as a multilay er condensation stare and physisorbed states in the form of a two-dime nsional 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 mole cules as the flux increases. (C) 1998 American Institute of Physics. [ S0021-3640(98)01411-X].