Full and half collisions

The decay of the complex is described by exactly the same equations of motion independent of its creation, namely Hamilton s equations in classical mechanics and Schrodinger s equations in quantum mechanics. Only the initial conditions for the ultimate fragmentation step are different because they reflect how the intermediate complex was formed. However, these differences lead to several important implications  

Under normal conditions for an atom-molecule collision the summation over J extends over many (of the order of one hundred or even more) so-called partial waves which makes the practical calculation rather cumbersome. An even more serious problem is the substantial blurring of distinct dynamical structures such as quantum mechanical interferences or resonances. Since these structures depend parametrically on J, the summation over all possible J values rapidly washes out finer details. 

Excitation with a photon, on the other hand, is subject to the dipole selection rule (see Chapter 11) 

Furthermore, the total energy Ef in half collisions can be relatively easily controlled by variation of the photolysis wavelength. This is essential for the detection of resonances and other structures which require high 

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