Photoionization direct

For many years, investigations on the electronic structure of organic radical cations in general, and of polyenes in particular, were dominated by PE spectroscopy which represented by far the most copious source of data on this subject. Consequently, attention was focussed mainly on those excited states of radical ions which can be formed by direct photoionization. However, promotion of electrons into virtual MOs of radical cations is also possible, but as the corresponding excited states cannot be attained by a one-photon process from the neutral molecule they do not manifest themselves in PE spectra. On the other hand, they can be reached by electronic excitation of the radical cations, provided that the corresponding transitions are allowed by electric-dipole selection rules. As will be shown in Section III.C, the description of such states requires an extension of the simple models used in Section n, but before going into this, we would like to discuss them in a qualitative way and give a brief account of experimental techniques used to study them. 

Fig. 1. Relationship between direct photoionization and shake up and shake off phenomena for core levels...

Shake up - shake off satellites. Monopole excited states energy separation with respect to direct photoionization peaks and relative intensities of components of singlet and triplet origin. Short and longer range effects directly (Analogue of UV). 

The first levels of information available derive from the measurement of absolute and relative binding energies and relative peak intensities. The distinctive nature of core levels means that identification of elements is straightforward as is the distinction between peaks arising from direct photoionization and Auger processes. 

Fig. 51. Plot of ratio of area ratios for direct photoionization peak and tow energy shake up satellite for a series of alkane styrene copolymers as a function of chain length n of the alkane component...

The Kf matrix is related to the conventional K matrix of MQDT by a frame transformation from parabolic to spherical co-ordinates the K matrix is then related by a further frame transformation to the quantum defects [43, 45], The first term in Eq. (4) gives a contribution to the photoionization intensity borrowed from the bound-state spectrum. The dlyom term represents direct photoionization, and the overall expression allows Fano-type interference between these terms. In Eq. (5) A is a phase shift in the parabolic rep-... 

Does the kinetic evidence from studying the reaction mechanism support this, or favor instead a direct photoionization ... 

For autoionization following inner-shell excitation such a classification neglects the competing and interfering process of direct photoionization leading to the same final state. It would be more appropriate to consider autoionization as a resonance feature embedded in the ionization continuum of main and satellite photoprocesses. 

Hitherto the discussion of Fig. 5.2 has neglected the possibility of non-radiative decay following 4d shell excitation/ionization. These processes are explained with the help of Fig. 5.2(h) which also reproduces the photoelectron emission discussed above, because both photo- and autoionization/Auger electrons will finally yield the observed pattern of electron emission. (In this context it should be noted that in general such direct photoionization and non-radiative decay processes will interfere (see below).) As can be inferred from Fig. 5.2(h), two distinct features arise from non-radiative decay of 4d excitation/ionization. First, 4d -> n/ resonance excitation, indicated on the photon energy scale on the left-hand side, populates certain outer-shell satellites, the so-called resonance Auger transitions (see below), via autoionization decay. An example of special interest in the present context is given by... 

In the presence of a dopant in the positive ion mode, the first step of the ionization process is the production of a radical ion from the dopant molecule by direct photoionization ... 

Thus, besides the direct photoionization, the analytes in positive APPI mode are ionized either by charge exchange or by proton transfer. The direct ionization and the charge exchange processes allow the ionization of non-polar compounds. This is not possible either with APCI or ESI. 

The production of both 0+(2Z)) and 0+(2P) occurs in the dayglow through direct photoionization,... 

While it is difficult to ensure the rehable observation of the radical processes during the mixing of reagents, these are easily detected in the photoinduced reactions of aryl-substituted compounds of Ge and Sn. Laser pulse photolysis experiments show that direct photoionization of Ph3Ge(Sn) anion results in the neutral radical . The apphcation of the Chemically Induced Dynamic Electron Polarization (CIDEP) method has allowed the detection of polarized emission signal of the radicals, thus leading to a conclusion that direct photoionization of Ph3Ge(Sn) anion occurs from the triplet state (equation 7). ... 

The PS spectrum has a strong peak centered at 285 eV associated with the direct photoionization of the core levels and a low-energy satellite peak at 291.6 eV arising from shake-up transitions ( tt it ) accompanying core ionization. These... 

Figure 10 Illustration of two channels for ionization of a d electron, direct photoionization, and photoabsorption followed by SCK decay...

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