[Legenda]  
[Contents of the thesis] 

[Comments on this module] 



[Legenda]  
[Contents of the thesis] 

[Comments on this module] 
In the measured differential cross sections of the process Na + I Na^{+} + I^{}, as shown in Fig. A08m5aF1,
Figure A08m5aF2: Polar differential cross section for chemiionization (CM system) at E_{i} = 13.1 eV, calculated in semiclassical approximation with the potential parameters of Table A08m5biT1 and the coupling parameters H_{12}=0.065 eV and H_{rot}=0 eV s. (a) Differential cross section with complete interference structure, calculated with the lowestorder stationaryphase approximation. The region of the classical rainbow angle has been omitted. (b) Differential cross section calculated with the stationaryphase approximation and uniform rainbow approximation showing separated the longwavelength interference structures due to a + c (, full curve), b + c (, full curve) and d + e (, dashed curve) interferences. (c) Full bars indicate the measured maxima of the interference structure on the differential cross section due to netattractive scattering. Dashed bars indicate the maxima due to netrepulsive scattering. 
We have calculated
the theoretical differential cross sections via the deflection curve
. The absolute value of the theoretical cross sections, which is shown in figure A08m5bii1F1
, is determined in the Quantitative interpretation, with the necessary potential parameters
. Here we consider the qualitative features of the calculated curve.
Figure A08m5aF3: Deflection curves for chemiionization scattering (CM system) at E_{i} = 13.1 eV 
Fig. A08m5aF2 demonstrates very clearly the tripartition of the theoretical cross section curve. The covalent scattering causes the narrow but high peak between 0 and 65 eV degree while the separated broader and lower part between 65 and 250 eV degree is due to ionic scattering. Both types of scattering supply small contributions to the very small differential cross section beyond the classical rainbow angle, due to netrepulsive scattering.
For covalent as well as ionic netattractive scattering the contributions to the cross section go to zero at because the deflection function for b b_{max}. In addition there is a sharp decreasing value of the transition probability P_{b} for b b_{max} caused by the decreasing value of the radial velocity of the colliding particles at the pseudocrossing R_{c}.
Eq. (E1)
=  
=  
(E1) 
shows that the differential cross section contains six superposed or only one interference oscillation depending whether four or two scattering trajectories contribute to the cross section.
An estimation of the wavelengths of the different
oscillations gives the result that only the interferences of a + c,
b + c and the d + e branches have a wavelength of a few eV degrees or
more on the scale and only that kind of structure could be detected
in our measurements
.
Because in our case a + c and b + c interferences never occur together, the differential cross section contains only one or two superposed interesting oscillations. In the case of two oscillations one occurs from netattractive scattering, the other one from netrepulsive scattering. Then, for our purpose, Eq. (E1) can be changed into:
(E2a) 
(E2b) 
(E2c) 
Actually Eqs. (2a) and (2c) for the theoretical differential cross section describe the Stueckelberg oscillations, that is the interference due to trajectories from different potentials. Those oscillations are shown in Fig. A08m5aF2b on the covalent scattering cross section peak and on the netrepulsive scattering differential cross section.
Eq. (2b) describes the interference of two contributions of ionic scattering, normally called rainbow scattering. The differential cross section shows the rainbow structure between and eV degree.
For the experimental differential cross sections, Fig. A08m5aF1 shows over a wide angular range all main features of the cross section of interest. The longwavelength Stueckelberg and rainbow oscillations due to netattractive scattering interference have been resolved completely while the repulsive (Stueckelberg) interference can be seen clearly beyond 250 eV degrees. In the range between 25 and 55 eV degrees there is some evidence of a double structure. Particularly on the 13.1 eV curve heavy and small maxima succeed each other and indicate a repulsive oscillation on that range with half the frequency of the attractive oscillation.
Thus the experimental and the theoretical differential cross sections of chemiionization in collisions between Na and I agree qualitatively.