Spin-independent scattering observables

To understand an electron—atom collision means to be able to calculate correctly the T-matrix elements for excitations from a completely-specified entrance channel to a completely-specified exit channel. Quantities that can be observed experimentally depend on bilinear combinations of T-matrix elements. For example the differential cross section (6.55) is given by the absolute squares of T-matrix elements summed and averaged over magnetic quantum numbers that are not observed in the final and initial states respectively. This chapter is concerned with differential and total cross sections and with quantities related to selected magnetic substates of the atom. 

The status for inelastic collisions is a little less satisfactory than for elastic collisions. CoIIisional excitation of atoms involves excited states with several magnetic substates. Standard total or differential cross section measurements sum over the magnetic substates, and thus give no information on the shape of the excited state and direction of the angular momentum transferred to the excited atom. These can be determined in 

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Spin-independent scattering observables 8.4 Two-electron atoms... 

A further effect is discussed in Chapter 5, namely that of spin-orbit scattering. This effect preserves the coherence of the two scattered waves but changes the constructive interference into a destructive one. The characteristic time tw is believed to be independent of Ty and inversely proportional to Z4, where Z is the atomic number. An analysis by Fukuyama and Hoshino (1981) shows that Ac depends on and leads to a behaviour as shown in Fig. 1.24. The negative part should be observed only for heavy metals. 

At the end of the 1970s proposals were made [G179] to measure a third, independent proton-nucleus elastic scattering observable, specifically the spin rotation parameter, which is referred to as 0. 

Thermal distributions of NO(u 2, J, A Ej,) states were observed, wherein the population in any level was determined by the internal energy and the parameter Tr. and independent of spin-orbit state or lambda doublet species. This is in contrast to the rotational rainbows, the propensities for preferential population in the Il(A ) lambda doublet species and the Fj spin orbit state which were observed in direct inelastic scattering of NO/Ag(l 11). 

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