Investigation of Gas–Solid Reactions by Modulated Molecular Beam Mass Spectrometry

Abstract

An apparatus for the study of gas-solid reactions which produce gaseous reaction products is described. The reactant gas contacts the solid as a molecular beam travelling in vacuum. Gaseous reaction products are monitored by a mass spectrometer as they are emitted from the surface. The technique relies heavily upon modulation of the molecular beam to improve the signal-to-noise ratio. In addition, chopping of the reactant beam induces modulation at the same frequency in the reaction products and the phase differences between these two signals contains important kinetic information. Methods of comparing theoretical models of the surface processes with the phase and amplitude information provided by the experiment are presented.