A new supersonic molecular beam line has been attached to an existing UHV apparatus. Three different nozzles mounted on a rotatable manipulator allow for independent gas feeds. In this way, dosing sequences with different reactive gases can be carried out within a few minutes. Due to the compact design of the beam line, the apparatus does not forfeit its original flexibility and mobility. Apart from standard techniques like thermal desorption spectroscopy, low-energy electron diffraction, reflection absorption infrared spectroscopy and x-ray photoelectron/Auger electron spectroscopy, a quadrupole mass spectrometer mounted on a linear drive and viewports allows for photochemical experiments or other laser applications