Coupling schemes photoionization

Within the two-step model, one can say that the intermediate photoionized state is the initial state for the Auger transition. For the K-LL spectrum of neon this initial state is described by ls2s22p6 2Sj/2. For the final state the possible electron configurations of the ion were shown in Fig. 2.5. Within the LS-coupling scheme which applies well to neon, these electron configurations yield the following final... 

The complete experiment for 2p photoionization in magnesium described previously depends on the validity of the non-relativistic LSJ-coupling scheme and on the existence of a simple subsequent Auger transition. However, such conditions are rarely met, since in heavier elements spin-orbit effects cannot be neglected, and for outer-shell photoionization no subsequent decay is possible. In order to perform a complete experiment for such cases,f measurement of the spin-polarization of the photoelectrons is necessary. As an example, 5p photoionization in xenon will be discussed. 

In this general formulation no information is required concerning the underlying coupling scheme used for the description of the photoionization channels. 

Figure 5. A femtosecond pump-probe photoionization scheme for studying excited-state dynamics in DT. The molecule is excited to its S> electronic origin with a pump pulse at 287 nm (4.32 eV). Due to nonadiabatic coupling, DT undergoes rapid internal conversion to the lower lying Si state (3.6eV). The excited-state evolution is monitored via single-photon ionization. As the ionization potential is 7.29 eV, all probe wavelengths <417 nm permit single-photon ionization of the excited state.

Although bond cleavage and photoionization are common processes occurring from upper excited states, the energy stored in these states can also facilitate the formation of new bonds. For example, multiphoton excitation of perylene and pyrene in cyclohexane leads to hydrogen abstraction from the solvent and subsequent radical coupling products [81]. Two-color irradiation of anthracene (47) in the presence of acrylonitrile leads to a four-fold increase in the amount of cycloadduct 101 as compared to that obtained under one-laser irradiation [52] (Scheme 7). That this is an upper triplet process was indicated by the triplet depletion... 

Photoionization out of several neutral states to several cation states may be simply included as separate terms of a split-operator scheme, assuming the ionized states do not strongly couple. Alternately, when the different ionization channels interact weakly, ionization out of each channel may be computed separately and the results combined. Examples of nonadiabatic dynamics seen through time-resolved photoelectron spectroscopy will be seen in Secs. 5.2 and 5.4. In the rest of this section, we will see examples of the diabatic representation for two classes of nonadiabatic interaction, the avoided crossing (Sec. 5.2.1.1) and the conical intersection (Sec. 5.2.1.2), and then discuss the necessary extensions to the standard vibrational wavefunction time-propagating schemes. 

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