21A1　U90 - (White Light) Chemical Dynamics (PRT 75%)

Endstations

Crossed Molecular Beam Machine

The crossed molecular beam machine established at 21A end station consists of three main parts: two rotatable source chambers, a reaction chamber, and an ion detector. The two source chambers fixed at 90^o to each other are rotatable from –20^o to 110/sup>o relative to the ion detector. For bimolecular reactions two molecular beams cross in the reaction chamber and for photodissociations a photolysis beam intersects a molecular beam. Reaction products after 10-cm free flight are ionized using synchrotron radiation. The desired ions are selected with a quadrupole mass filter and detected with a Daly-type ion counter. As a liquid nitrogen cooler combined with a He-refrigerator is used, the vacuum in the ionization region can be suppressed down to 5 x 10^-12 Torr which dramatically increases the signal-to-noise ratio in H2 detection.