Molecular beams velocity-vector diagram

CoMPABisoN OF REACTION KINEMATICS. Figure 4 compares the most probable threshold velocity vector diagrams for Reactions 4 and 6. For both diagrams, the velocity vector for the molecular beam is drawn to correspond to the most probable velocity at the temperature of the beam source used in the experiments (300 K for T2 and 77 K for H2). The atomic beam velocity is then drawn so that the relative collision... 

In crossed molecular beam experiments, measurements of the product angle and speed are taken in the laboratory coordinate system (LAB). But information in the center-of-mass coordinate system is required to explain the dynamics of the scattering process. Thus, the results obtained in the laboratory coordinate system must be transformed to the center-of-mass coordinate system. We usually use the Newton vector diagram, i.e., the velocity vector diagram. 

Figure 23.15 Product images of HCL(v = 0, J = 1 and J = 5) from the reaction of Cl with n-butane. The Newton diagram for the reaction is overlaid on the image of the Cl atom reactant. CM indicates the position of the centre of mass, the vectors VcLj and Vrh represent the CL2 and RH molecular beam velocities respectively Vci and i/q are the velocities of the Cl atoms in the Laboratory and centre-of-mass frame respectively Hciis the velocity of the product HCl in the centre-of-mass frame and 6 is the scattering angle. Reproduced from Toomes and KitsopouLos, Phys. Chem. Chem. Phys., 2003, 5 2A81, with permission of the PCCP Owner Societies...

The full Newton diagram is much more complicated than what is shown in Fig. 2. First, there is a set of secondary velocity vectors originating at the tip of every primary velocity vector. The circle corresponding to only one such set is shown. Second, although the detected laboratory velocity must be in the plane containing the molecular beam and detector axes (the plane of Fig. 2), the primary and secondary vectors may be out of this plane. For example, the primary step may be such that the fragment velocitj is out of the plane, but tbe secondary velocity may be such that the resultant... 

---