Photoionization schemes

Figure 1. (a) Schematic diagram of a laser photoion projection microscope and (b) spectrally selective multistep photoionization scheme for absorbing centers (color centers, molecular chromophores, etc.) by ultrashort laser pulses. 

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.

The photoionization scheme via the so-called auloionization state (AIS) is shown in Figure 4B. 

Traps are often used for accumulating ions, which are not so easy to produce, e.g. isotopes in nuclear physics applications. In the case of molecular ions this means that one may use also rather inefficient ways to create or to prepare them in specific states. So far photoionization schemes,... 

Fig. 2.20. Photoionization schemes, (a) Resonant 1 -i-1 REMPI, (b) nonresonant MPI, resonant 1 + 2 REMPI, and resonant 1 + 1 REMPI with two different wavelengths. Reproduced from Ref. [92] with permission. The Vacuum Society of Japan, 2007.

Qualitatively, the basic photoionization schemes may be classified as illustrated in Fig. 9.2. Excited states that are far from the ionization limit can, effectively, be ionized by laser radiation only. The following two possibilities exist in this case direct... 

Fig. 8.19 Schematic energy level diagrams showing possible LIS schemes. In each case the level scheme for just one isotope is shown. (Van Hook, W. A. in Vertes, A. Handbook of Nuclear Chemistry 5, 177 (2003)). (a) One photon molecular photopredissociation using a single laser, (b) Two photon photoionization using lasers of the same (right) or different (left) frequencies...

Figure 4.1 Detection by degenerate superposed absorber states, (a) Scheme of levels relevant to the pumping of the +) state and its photoionization by orthogonally polarized LO and SL fields, (b) Geometry of illumination, DC Stark mixing, and current directionality. The sample is divided by a potential barrier (dark rim) into two regions where separate currents arise for cross-correlation measurements, (c) The odd symmetry part (with respect to of the photoelectronic momentum distribution, which is responsible for Jy. and is associated widi die cross product of the fields.

This process can be accounted for in terms of a consecutive two-photon-induced ionization. Absorption of the first photon results in the formation of the 2AP singlet excited state, and absorption of the second photon causes photoionization according to the following scheme ... 

Fig, 1. Pump-probe photoionization (PPI) and time-resolved degenrate four-wave mixing (TRDFWM) schemes for rotational coherence spectroscopy (RCS). 

Figure 19. Excitation scheme for probing bound-free transitions. Initially the photoion of the mother molecule appears. After dissociation, however, the relating fragment ion is observed.

Silathietanes can be readily prepared from the appropriate bis(chloromethyl)silane and KSH or by intramolecular hydrosilation in the presence of Wilkinson s catalyst (Scheme 97) (81JOM(204)13). Electron impact and photoionization mass spectrometry support the loss of silathione ions (R2Si=S) (R = Me, Et) indicating a transannular interaction, though decomposition by the loss of silenes and thioaldehyde also readily occurs (81JOM(214)145). 

Intense laser sources have been used to induce ionization or fluorescence of products in several kinds of photolytic experiments. Welge and his colleagues have used these sources to detect NO by multiphoton ionization (MPI) of the product. They have also used lasers that have been extended to the VUV region by various nonlinear mixing schemes as photoionization sources for mass spectrometric detection of reaction products. 

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. 

In the D-region, the primary positive ions are NO+ and 02 (NO+ being dominant) and so the problem reduces to one of finding a quantitative chemical scheme for the conversion of NO+ to H30+(H20)n ions, the steps of which are sufficiently rapid to remove NO+ at a rate commensurate with its known production rate from photoionization of NO. The first proposal was made by Fehsenfeld and Ferguson63) who, with their colleagues, have contributed so much to this area of research. Their scheme, based on their FA data, is summarised by the following reactions, the first step being the direct 3-body hydration of NO+ ... 

An example of the bimolecular photoionization of the excited singlet molecule given by Eq. (3.330) can be represented by the following comprehensive scheme ... 

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