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Treated results: Experimental differential cross section=A08-m4bi1

On the chemi-ionization collisional process of sodium atoms on iodine atoms measurements have been done [particulars on the measurements in the Experimental methods module (link type: 'depends on/essay-back'; target: A08-m3a)] in the kinetic-energy range from 13 up to 85 eV. Fig. A08-m4bi1-F1 shows relative polar differential cross sections of collisions with initial relative kinetic energies Ei of 13.1 and 18.2 eV.

[To the FULL figure] Figure A08-m4bi1-F1: Relative polar differential cross section for chemi-ionization (CM system). The cross sections, measured at a colliding energy of 13.1 and 18.2 eV, have been set in scales with shifted zero points

The general shape of the differential cross section has been measured at collision energies of 13.1, 20.7, 29.7, 38.7 and 55.0 eV, as shown in Figs.  A08-m4bi1-F2 a, b, c, d, e. [Compare these results to the theoretical results (link type: 'compare'; target: A08-m4bii2].
[To the FULL figure] Figure A08-m4bi1-F2: Smoothed differential cross sections for five different collision energies. (a), (b), (c), (d), (e): Full curves show the measured relative differential cross section, averaged over the interference structures

Data analysis and presentation

The transformation of the raw data of the detector signal [(link type: 'depends on'; target: A08-m4ai1] into the differential cross section needs the effective size of the collision region as a function of the scattering angle [This effective size is determined by the Experimental methods (link type: 'depends on'; target: A08-m3a].

A priori there are doubts on the normalization of the detector signal to an angular-independent scattering volume viewed by the detector. The calculated angular-dependent normalization factor seems to be reliable by observing the result that the total cross section due to covalent scattering is about equal to the total cross section due to ionic scattering, independent of the kinetic energy and thus independent of the different angular ranges. This requirement is postulated by the equal Landau-Zener probability Pb(1 - Pb) for both chemi-ionization trajectories and means about equal areas enclosed by the relevant parts of the differential cross section [Why these cross sections are equal is explained in a mesoscopic Theoretical methods module  (link type: 'explained in/To cause/wider range/project'; target: MESO-m3c-mod].

Actually the iodine oven [Particulars on the oven are given in a mesoscopic Experimental methods module (link type: 'depends on/is detailed in/wider range/project'; target: MESO-m3a-I] is a hybrid between a collision chamber and a secondary beam with a collision region neither large nor small as compared to the field of view of the detector . The effective size simply has been calculated geometrically for all angular resolutions and angular positions of the detector supposing that there is no gas density gradient inside the inner tantalum cylinder of the oven and a zero density outside.

This calculation leads to correct normalization curves since the measurements given in Fig.  . The measurements are only relative and have been given for the different energies on arbitrary, non-related scales. Because of the large differences in intensity, the curves in figure F1 have been divided into three parts (with small overlaps') and have been multiplied by the factors 1/3, 1 and 5. The reproducible interference structure due mainly to net-attractive scattering, has been indicated by full lines. The reproducible maxima of the interference structure due to net-repulsive scattering have been indicated by arrows.

The angular resolution of the detector used for the several angular ranges is shown at the top of figure F1. The bar above the angular-resolution number means that on the relevant range the measured points have been substituted by an equal number interstitial points to reduce the statistical noise in order to show the fine structure more clearly.

Reliability

Figure A08-m4bi1-F1 shows the applied angular resolution for the various stages. Going up in scattering angle the sharply decreased detector signal requires a decreasing angular resolution.

Determination of complete and resolved differential cross sections at lower kinetic energies is prevented by the quickly decreasing intensity of the sodium beam while the apparatus is not suitable to resolve the structure at small scattering angles at kinetic energies above 20 eV. [The restrictions of the set-up are given in the module Experimental methods (link type: 'depends on'; target: A08-m3a].