Crossed Molecular Beam Machine
The crossed molecular beam machine established at 21A end station consists of
three components, the rotating source chamber, main chamber and detector. Two
source chambers fixed at 90° to each other are rotatable with respect to the
detector. For a bimolecular reaction two molecular beams will cross in the main
chamber and for a photodissociation reaction a molecular beam will intersect
with a photolysis beam. Reaction products after 10 cm free flight will be
ionized with the synchrotron radiation. The desired ions are selected with a
quadruple mass filter and then detected by a Daly-type ion counter. The
background pressure in the ionization region can be suppressed down to 5×10-12
Torr which makes H2 product measurement doable as a liquid nitrogen
cooler combined with a He-refrigerator is used.
U9 White Light Beamline
In this crossed molecular beam machine, reaction products are ionized using VUV
photons instead of conventional electron impact method. One of the advantages
is to suppress dissociative ionizations as a proper ionization wavelength is
used. An insertion device U9-undulator installed in the storage ring is
employed to generate a multiple-harmonics light source. Only the first harmonic
photons are desired thus a trickily designed gas cell filling with noble gas is
used to absorb high order harmonic light. The output wavelength can be tuned by
adjusting the gap of undulator. At this beamline a typical resolution E/ΔE
20
and a photon flux
1×1016
photons/sec can be offered for the photon ionization.
Schematic of high-harmonics light absorption cell.
The upper right device is used to make turbulence
at the output of gas cell.