Molecular beam crossed, generation

The setup used for crossed beam experiments is basically the same apparatus used in the H2O photodissociation studies but slightly modified. In the crossed beam study of the 0(1D) + H2 — OH + H reaction and the H + HD(D2) — H2(HD) + D reaction, two parallel molecular beams (H2 and O2) were generated with similar pulsed valves. The 0(1D) atom beam was produced by the 157 photodissociation of the O2 molecule through the Schumann-Runge band. The 0(1D) beam was then crossed at 90° with the... 

H2 molecular beam. The H-atom products were detected by the Rydberg tagging TOF technique using the same scheme described in the last paragraph with a rotatable MCP detector. Figure 4 shows the experimental scheme of the crossed beam setup for the 0(1D) + H2 reactive scattering studies. The scheme used for the H + D2(HD) studies is very similar to that used in the 0(1D) + H2 except that the H-atom beam source is generated from HI photodissociation rather than the 0(1D)-atom beam source from 02 photodissociation. 

These requirements can be met in a so-called crossed molecular-beam experiment, which is sketched in Fig. 2.1.1. Here we can generate beams of molecules with well-defined velocities and it is possible to determine the speed of the product molecules, e.g., vc = vc, by the so-called time-of-Sight technique. The elimination of multiple scattering in the reaction zone and collisions in the beams are obtained by doing the experiments in high vacuum, that is, at very low pressures. 

In Sec. 8.2 we discussed the production of cold molecules from a single collision with an atom. It was noted that the cold molecules are necessarily formed at the crossing of the atomic and molecular beams, where the scattering occurs. To date we have put considerable effort to understanding the practical and experimental limits of the crossed molecular beam apparatus for producing cold molecules and what modifications we need and can make in order to produce and confine useful amounts of cold molecules generated from this kinematic cooling technique. 

Chandler and colleagues studied the bimolecular reaction H-i-D2 D-hHD. In their study, an atomic hydrogen beam (generated through the photolysis of HI) of well-defined velocity was crossed with a molecular beam of D2. The velocity distribution of the deuterium atoms formed in the reaction was studied at two different centre-of-mass collision energies of 0.54 and 1.29 eV. Figure 6 shows the D... 

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