Electronic excitation section Scattering

Electrons interact with solid surfaces by elastic and inelastic scattering, and these interactions are employed in electron spectroscopy. For example, electrons that elastically scatter will diffract from a single-crystal lattice. The diffraction pattern can be used as a means of stnictural detenuination, as in FEED. Electrons scatter inelastically by inducing electronic and vibrational excitations in the surface region. These losses fonu the basis of electron energy loss spectroscopy (EELS). An incident electron can also knock out an iimer-shell, or core, electron from an atom in the solid that will, in turn, initiate an Auger process. Electrons can also be used to induce stimulated desorption, as described in section Al.7.5.6. 

Being formed in the gaseous phase medium, the electronically excited particles (EEPs) reach the solid surface by diffusion. The diffusion coefficients of EEPs are, as a rule, smaller than the self-diffusion coefficients of parent gas, a factor that is associated with increasing of the EEP elastic scattering cross-section at parent molecules due to the redis-... 

In Section IV we quantify the relation of the information-rich phase of the scattering wavefunction to the observable 8(E) of Eq. (5). Here we proceed by connecting the two-pathway method with several other phase-sensitive experiments. Consider first excitation from g) into an electronically excited bound state with a sufficiently broad pulse to span two levels, Ea and ),... 

The total positron scattering cross section, erT, is the sum of the partial cross sections for all the scattering channels available to the projectile, which may include elastic scattering, positronium formation, excitation, ionization and positron-electron annihilation. Elastic scattering and annihilation are always possible, but the cross section for the latter process is typically 10-2O-10-22 cm2, so that its contribution to erT is negligible except in the limit of zero positron energy. All these processes are discussed in greater detail in Chapters 3-6. 

Fig. 2.14. Compendium of total cross section data for positron-noble gas and electron-noble gas scattering. The arrows refer to thresholds for (in order of increasing energy) positronium formation (positrons only), excitation and ionization. (From Kauppila and Stein, 1982.)...

Here, m and n denote the initial and final states, respectively, of the electronic ground state. Although not explicit in Eq. (1-62), e represents an electronic excited state (Fig. 1 -28) involved in Raman scattering, /o is the intensity of the incident laser beam of frequency vo. The (v0 - vm )4 term expresses the v4 rule to be discussed in Chapter 2, Section 2.6. Finally o.pa)mn represents the change in polarizability a caused by the m —> e —> n transition, and p and a are x, y and z components of the polarizability tensor (Section 1.7). This term can be rewritten as (38)... 

This section discusses applications of IR and Raman spectroscopy to materials with reasonable or even very high conductivity. These systems generally present special problems in addition to those described in earlier sections. Incident radiation interacts not only with the vibrational excitations of the material but also with the free carriers and with its electronic structure. These interactions may create phenomena such as free carrier absorption, excitation across the energy gap, exciton transitions, or light scattering by free electrons. Excitations are very often in the IR spectral range, particularly in the... 

The influence of electronic excitation and curve crossing on elastic scattering is very important. In general, it is typical for atom-atom or atom-ion scattering at high energies and is discussed in Section III.B and IV.B.3. Thus... 

The differential elastic cross section for scattering of potassium on several halogen compounds has been measured between 1 and 100 eV103104 in order to get information on the curve crossing between the ionic and covalent configuration in these systems. This experimental approach could also be used in cases where electronic excitation is important. 

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