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Qualitative interpretation=A05-m5aii

In the measured differential cross section of the chemi-ioniation reaction M + X2 M+ + X- a small maximum is observed in the small-angle region, seen in all cross-section curves,
figure of the cross sections given in A05-m4bi
that cannot be explained [Compare with the classical interpretation (link type: IS COMPARED WITH/sq-back; target:  A05-m5ai)] by a classical model stating the general shape of the deflection curve as sketched in figure A05-m5aii-F2
[Unfold the general shape of the deflection function as given in MESO-m3c-defl]
and the equation for the differential cross section [The equation is imported from the mesoscopic theoretical methods (link type: INPUT FROM/is elaborated in/wider range/project; target:  MESO-m3c-defl)]  
$\displaystyle I(\theta)=\frac{1}{\sin \, \theta}\sum_{i=1,2,\ldots}\
P_{b_{i}}(1-P_{b_{i}})b_{i}\bigg\vert\frac{\dr b_{i}}{\dr {{\mit\Theta}.
}}\bigg\vert.$     (E1)

Quantum mechanically this phenomenon can be explained by constructive interference of some contributions, for instance the contributions of the two net repulsive branches of the b-$\tau $ curve. Because of the nearly equal slopes and about equal collision parameters of these branches at small scattering angles, the wavelength of the interference is rather long; a rough estimate has shown that the wavelength has a value of a few degrees at the energies used, which is of the same order of magnitude as the widths of the measured maxima.
[unfold details estimation.

Although we have only considered a two-contribution interference instead of four contributions, this interference can explain the observed bump in the differential cross section at small angle.