of the thesis]
[Comments on this module]
of the thesis]
[Comments on this module]
We determine the potential parameters that govern the chemi-ionization reaction Na + I Na+ + I We now restrict ourselves as much as possible to the determination of some
potential parameters and to the comparison of
measurements and calculations used for that purpose. The calculated differential cross section and its discrepancies with the measurements will be treated in module Quantitative interpretation A08-m5bii
Figure A08-m5bi-F1: Polar differential cross section for chemi-ionization (CM
system) at Ei=13.1 eV. (b) Differential cross section calculated with the stationary-phase
approximation and uniform rainbow approximation showing separated the
long-wavelength 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 net-attractive scattering. Dashed bars indicate
the maxima due to net-repulsive scattering.
We now restrict ourselves as much as possible to the determination of some potential parameters and to the comparison of measurements and calculations used for that purpose. The calculated differential cross section and its discrepancies with the measurements will be treated in module Quantitative interpretation A08-m5bii .
Fig. A08-m5bi-F1b shows the differential cross section with simplified interference structure. An additional simplification in Fig. A08-m5bi-F1b is the separate reproduction of the attractive and repulsive scattering contribution as though they could be distinguished. Because the origin of the oscillatory features of the calculated cross sections can be seen easily from Fig. A08-m5bi-F1b and the latter figure is more easily related to the deflection function and the potential curves, Fig. A08-m5bi-F1b is more suitable to fit the interference structure of the calculated and measured differential cross section by adjustment of the potential parameters. Moreover, convolution of the differential cross section of the complete calculated cross section, which is given in Fig. A08-m5bi-F1a , and Fig. A08-m5bi-F1b even with the smallest angular resolution of the detector of 0.3º fwhm will lead to equal results.
By comparison of measurements and calculations, the missing parameters of the covalent potential curve and the value of H12 can be estimated. For that purpose are very important particularly the wavelengths of the rainbow and Stueckelberg oscillations , which result from the semi-classical interference of different contributions to the scattering angle .
For a fitting procedure of the potential curves to the measurements, it is very helpful that the interference wavelengths can be estimated directly from the deflection curves. The oscillations are generated by the cosine of the Eqs. (E1)
|Figure A08-m5bi-F2: Deflection curves for chemi-ionization scattering (CM system) at Ei=13.1 eV.|
|Figure A08-m5bi-F4: Na_I adiabatic potential curves. The pseudo-crossing potentials are all of the same species . [Copied to the Treated results (link type: 'output to'; target: A08-m4bii1)]|
|Figure A08-m5bi-F3: Wavelength of the oscillatory differential cross section (CM system) due to net-repulsive scattering, versus the colliding energy. The measurement give the wavelength averaged over ten oscillations just beyond the rainbow angle. The error bars only indicate the error in the relative position of first and tenth oscillation. The curve gives the corresponding calculated wavelengths|
The ionic potential curve is overdefined by the given parameters. That is why the values for A and re have not been used but the other parameters give rise to the values given in parentheses.
For small values of the internuclear distance R the ionic and covalent potential curves bend over to negative values, leading to . This is due only to the mathematical form of the potential-energy expressions [Eqs. (E3) and (E4)]. Using the parameters of Table A08-m5bi-T1, the maxima of the potential curves are Uion=29.7 eV and Ucov=21.4 eV for R=1.16 Å and R=1.70 Å, respectively. However, this effect does not handicap the calculations. Even for the smallest impact parameter considered, the distances of closest approach are R0=2.02 Å and R0= 2.84 Å corresponding to the potential energies Ucov=-0.3 eV and Ucov=2.7 eV, respectively.