Our research program in environmental molecular science mostly deals with physics an chemistry of ice. Our team develops technics in surface science to elucidate natural phenomena using models reproduced in the laboratory. We have conceived and built this UHV (P<10-9 torr) setup that has two molecular beam sources, a mass spectrometer (Balzers Prisma ; 1-100 uma), a cryogenic sample holder with 4 axes (APD Displex 202B; T>20K), and a particle beam weapon (VG EX03), that enables to study elementary physico-chemical mecanisms implied in heterogeneous atmospherical chemistry. This setup allows us to investigate in situ how molecules transform when interacting with ice using the infrared spectroscopy (Nicolet Nexus 670). We can also study photo-chemical reactions using a 1000W Xenon lamp (Newport). Numerical simulations as well as molecular modelisation helps us to understand the mecanisms of the surface reactions at the molecular level.