We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
Published online by Cambridge University Press: 15 December 2009
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.
In the study of electron–atom collisions there has been a constant emphasis on increasing the state selectivity of the particles in both the initial and final states. Thus while total cross section measurements define the initial kinetic energies, measurements of differential cross sections as a function of angle give additional information on the final momentum states of the separating particles. Added state selectivity is obtained through the use of spin-polarised electrons, or spin-polarised atoms, and with spin analysis of scattered particles (see e.g. Kessler (1985)). The great progress that has been made with the use of spin-selected particles will be discussed in the next chapter. Much of the progress that has been made has been for the case of elastic scattering.
Collisional alignment and orientation
The status for inelastic collisions is a little less satisfactory than for elastic collisions. Collisional excitation of atoms involves excited states with several magnetic substates.
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.
