Schematic top-view of VENUS. The apparatus includes three gas beams (B1, B2, and B3), collimated on the gold surface of the main chamber by three series of diaphragms. A quadrupole mass spectrometer with a residual gas analyser (QMS-RGA) is situated within the chamber n°1 (CH1) to monitor the stability, composition, and purity of the gas flows during the course of an experiment. A second deposition system is connected to the main chamber (CHP) to enable background vapor deposition. The pressures in CH1 and CH2 are 10⁻⁸ and 10⁻⁹ hPa, respectively, and the pressure in CHP reaches 10⁻¹⁰ hPa. Atoms or molecules deposited on the surface can be quantified by the FT-RAIRS system during deposition and/or by the QMS in the main chamber, which is positioned in front of the surface, and a TPD can be performed.