Fig. 2

Schematic representation of the experimental setup. A discharge valve is used for the production of molecular beams of internally cold OH radicals. A skimmer with an orifice of 3 mm diameter is placed between the valve and the Stark decelerator. The beam of OH molecules is detected by laser-induced fluorescence (LIF) either 5 cm downstream from the nozzle or 11.5 mm after the exit of the 124-stage Sark decelerator. Stray light is reduced by aligning the 282 nm-excitation laser beam through Brewster windows. Light baffles limit its diameter to 3 mm. LIF at 313 nm is collected on a photomultiplier tube (PMT) using a lens and a stack of bandpass optical filters