The base pressure of the gas-handling system is < 1 × 10-4 Torr, the lower limit of the convectron (Granville-Phillips model 275). Opening the gate valve immediately after pumping 1 Torr of methanol out of the gas handling system produces a pressure rise of ~ 1 × 10-10 Torr in the UHV chamber, suggesting that the UHV chamber suffers negligible contamination from the gas handling system due to this design.
Prior to a reactant gas being used, the gas-handling lines are flushed with that gas three times and then pumped out via the turbomolecular and rotary vane pumps. A pressure between 0.5 and 1 torr of the gas is then isolated in the upper left-hand line. Prior to experimentation, mass spectra of the gas are taken to check for purity. Dosing of the reactant gas onto the clean Mo(110) surface at 100 K is carried out by direct dosers with precision leak valves.
