Excitation of Valence Electrons

8 eV against T= 4.49 eV of a core-excited Rydberg state (see above and p. 147) [1 ]. An ai(4s) Rydberg orbital (instead of an antibonding a valence orbital) had been proposed in [5, 6] to account for earlier observations of a discrete (instead of a continuous) band structure. The discrete structure was, however, not confirmed [15] (see also Phosphor C, 1965, p. 23), but a more recent MPI study using a dye laser revealed almost twenty bands at 351 to 398 nm, which could be assigned as (2+1) excitation via the A state [16]. 

leading to a A state [6]. Term values of T=17530 cm for PH3 and 17900 cm for PD3 (for a transition 4p 5a ) had been based [10] upon these latter energies [6,9] T=17900 cm- [11]. A long, single progression observed by EELS between 8 and 9 eV was more recently attributed to a transition 4p 5ai [11- 

Transition 5p 5ai( ). Resonance-enhanced MPl spectra (3-photon excitation) revealed a progression in for both PH3 (first band at 71000 cnrr ) and PD3 (71 622 crrr ). The assignment to 5p -5ai was based on quantum defects it contradicted, however, to a more ready 3-photon (than 2-photon) excitation [3]. MPl measurements (3-photon excitation) of four PH3 bands in this region pointed to an adiabatic energy of 75567 cm [16]. The PD3 progression had been earlier observed with its first band at 74 946 cm [6,9] see also E =75 000 cm (for a D state) in [4]. A term value of - 5800 cm for a transition 5p -5ai was based on this earlier measurement [10]. 

Transition 4p -2e. Photoabsorption using synchrotron radiation revealed a vibrational progression (in Vg) beginning at 80370 cm and another one (with additional excitation of the stretching vibration vi) beginning at 82713 cm The tentative assignment was based on quantum defects [2]. 

Vertical excitation energies of the singlet and triplet states and A, resulting from transitions of the 5ai electron to the orbitals 4s through 7s, 4p to 6p, 3d, and 4d, were calculated by a one-center expansion approximation [17]. 

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The impact of a UV/Visible photon on an isolated molecule modifies the term ciec in equation (11.1), determining the quantification and variation of its total mechanical energy. This electronic perturbation is also accompanied by modification in the terms rot and vib that correspond to the transition. Many such transitions are possible within the same molecule (Fig. 11.2). These transitions are related to the excitation of valence electrons. 

Both theoretical122-124 and experimental125 studies of the behavior of f0n versus q show that at qa0 < 1 the oscillator strengths for optically allowed transitions rapidly fall with increase of q, which is in agreement with formula (4.27). However, at qa0 > 1 the behavior of/0n( ) depends on the type of a transition. In the case of Rydberg transitions, f0n(q) has characteristic maxima and minima that are absent in the case of excitation of valence electrons. According to Ref. 123, their appearance is due to the existence of nodes in molecular orbitals. 

The properties of the target are described by its dielectric function s(k, a>), where hk and Hm represent the momentum and energy transfer to the system in an elementary inelastic process. This approach has the possibility of describing in a condensed way the screening of the intruder ions as well as the excitations of valence electrons in the solid, including both collective and single-particle (or electron-hole) excitations [13,14]. The stopping power in... 

The XPS spectra of La, Ce, Pr, and Nd are shown in fig. 3.53 (Baer and Busch, 1973). The metal La has no 4f electron, so the peak just below Ep comes from excitations of valence electrons. The sharpness of the leading edge, about 1 eV, is a measure of the resolution width. The width of the valence band, somewhat less than 5 eV, is in good agreement with the calculated value 3.5 eV (Fleming et al., 1968). The structure below 5eV corresponds to 5p electron excitations by an X-ray satellite. The spectrum of Ce shows a broader peak... 

Valence-shell electrons can also undergo transitions of three types, depending on their destination in this case, all are observable in practice. Valence-valence excitations and valence-virtual excitations can be considered together, and give rise to valence-electron excitation spectra. The excitation of valence electrons into the ionization continuum gives rise to valence-electron photoelectron spectra. The valence levels are greatly affected by molecule formation, as this is where the bonding actually occurs. 

For certain compounds, the photoejection of an electron from a core level may be accompanied by excitation of valence electrons. The kinetic energy of the photoelectron is reduced accordingly and a so-called shake-up satellite appears at a higher binding energy with respect to the parent peak. For aromatic organic materials, a shake-up structure with intensities of up to 5-10% of the main peak, due to %-% transition, is visible. This is illustrated by the C Is and 0 1s peaks of a commercial sample of poly(ethylene terephthalate) (PET) presented in Fig. 15. ... 

In addition to the structural defects, crystals also contain electronic defects, i.e. electrons and electron holes that are relatively free to move in the crystal. The electronic defects may either be formed through internal excitation of valence electrons or they may be formed in association with point defects. If these electronic defects are localised (trapped) at regular sites in the structure, the electronic defects are termed polarons or - from a chemical point of view - valence defects. Defect electrons or electron holes trapped at point defects often make otherwise transparent materials coloured, and composite defects involving point defects and trapped electronic defects are termed colour centres. 

The excitation/de-excitation of valence electrons, whether core hole induced or otherwise, are discussed in Section 3.3.2.3.2. 

The low-loss peak corresponds to the excitation of valence electrons n + cr). Recent studies showed that the plasmon peak is of particular interest in the study of mechanical and physical properties of materials [33]. A correlation between the plasmon maximum energy... 

Shake-up satellites Excitation of valence electrons (that accompanies relaxation processes) to an unfilled level at higher binding energy. The loss of kinetic energy of the outgoing photoelectron into a discrete... 

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