Surface reactivity by gas introduction in Knudsen cell mass spectrometry

Conditions for controlled gas flow introduction in an effusion cell are calculated according to different flow regimes that can be encountered in the gas line and its connection to a Knudsen cell. Molecular, transition, viscous and chocked flow regimes are analyzed in order to propose a general structure of the connection with the use of a small nozzle at the entrance of the Knudsen cell. Tests are then performed when introducing N2 gas and monitoring by mass spectrometry its pressure in the cell. An example of gas surface reaction-C gasification by O2 gas-is also presented.