Molecular chemistry angular distributions

Figure 21.1 Comparison of molecular and hydrodynamic beam sources. M is the flow Mach number. Top angular distribution for a thermal oven M = 0), a nozzle (M = 10), and a channel beam (CB). Bottom velocity distribution for a thermal oven and a nozzle beam the curves are normalized to the same maximum intensity. Reproduced from Toennies, i n Physicat Chemistry, An Advanced Treatise, VI-A, 1974, with permission of Elsevier...

Two distinct experimental approaches can be used for investigating photodissociation processes at the gas-solid interface, depending on the nature of the observable. In the first approach, speed, angular distribution, and internal excitation of the photofragments leaving the surface are measured. In the second approach, the photoproduct left behind at the surface is monitored. In the second approach, the standard tools of surface science are used. Surface photochemical studies usually require ultra-high vacuum (UHV) conditions, of the order 10 ° to 10 mbar. Initially, the adsorption and thermal behaviour of the molecule-metal system must be characterized. Various surface-science tools can be used to provide information about adsorption geometry, molecular structure and thermal chemistry of adsorbates. 

Grimley, R.T., Wagner, L.C., Castle, P.M. (1975) Angular distributions of molecular species effusing from near-ideai orifices. The Journal of Physical Chemistry, 79, 302-308. 

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