Photoionization conclusion

In this contribution, in order to illustrate tlie importance of shake-up bands for extended systems, we simulate and compare on correlated grounds the ionization spectra of polyethylene and poly acetylene, the most simplest systems one can consider to represent insulating or semi-conducting polymers. Conclusions for the infinite stereoregular chains are drawn by exU apolation of the trends observed with the first terms of the related n-alkane or acene series, CnH2n+2 and CnHn+2. respectively, with n=2, 4, 6 and 8. Our simulations are also compared to X-ray photoionization spectra (7) recorded on gas phase samples of ethylene, butadiene and hexatriene, which provide a clear experimental manisfestation of the construction of correlation bands (8-12). 

The apparatus has been already described in Ref. [7]. The clusters are produced by laser vaporization of a sodium rod, with helium at about 5 bars as a carrier gas and a small amount of SF6. The repetition rate is 10 Hz. In this configuration, the vibrationnal temperature of the formed clusters is roughly 400 K,[10] that gives 85% of C2V geometry and 15% of C3V for a Boltzman distribution. The laser beams are focused onto the cluster beam between the first two plates of an axial Wiley Mac-Laren Time-Of-Flight mass spectrometer with a reflectron. The photoionization efficiency curve as well as the photoabsorption spectrum determined by a photodepletion experiement are displayed on Fig. 1(b) and 1(c) respectively. The ionization threshold is at 4.3 eV, close to the 4.4 eV calculated for the C3V isomer and 4.9 eV for the C2V isomer (see the Fig. 1 (b)). The conclusion arising out of the photodepletion spectrum shown on Fig 1(c) and from ab initio calculations of the excited states, [5] is that the observed... 

In conclusion I would like to emphasize that the suggested approach (femtosecond laser spectromicroscopy) is not a simple modification of the Muller microscope [6], for the electric field here is not the decisive factor but serves solely to form the image. Table I lists the comparative characteristics of the Muller projection field-ion microscope (FIM) and proposed laser resonance photoelectron (photoion) spectromicroscope (LRFSM). 

Photoionization at 193 nm in oxygenated solution of poly(C) causes strand breakage with high efficiency, half of which occurs at times < 4 ms, the other half with a half-life of 7 ms (Melvin et al. 1996 Table 11.8). This kinetic behavior is very different from what is seen after -OH-attack and points to the direct involvement of the Cyt radical cation. In poly(U), the (biphotonic) photoionization shows similar results (Table 11.8). With poly(A), the formation of strand breaks is 20-times less efficient as compared to poly(C) (Table 11.8), and this is in agreement with the above conclusion that the A-+ or A- do not cause strand breakage to any major extent. 

The statement that there is good agreement between theoretical and experimental data is conventionally the conclusion drawn from the results presented. However, a deeper insight can be obtained when the dipole matrix elements involved are determined experimentally, and compared with results from different theoretical approximations of the influences of electron-electron interactions. In order to make such a comparison, the experimental matrix elements will be derived first for the case of 2p photoionization in magnesium at 80 eV photon energy. From equs. (5.14), (5.15), and (5.16) one can calculate DS, Dd and A from the measured observables. The results are listed in Table 5.1, together with data from several theoretical calculations. 

The solution to this apparent paradox lies in the photoionization dynamics. Clearly, the form of the parent ion signal depends strongly on the specific photoionization dynamics and, in order to avoid misleading conclusions, must be analyzed for each specific case. The (Koopmans) photoionization correlations of excited-state electronic configurations with those of the cation play a critical role. 

In conclusion, much interest is presently focussed on the dynamics and excitation spectra of transition-metal carbonyls and adsorbate systems, and I have little doubt that the problems discussed in this section will be understood before long. However, the problem of first principles descriptions of photoionization spectra of these systems will remain a very important field of application of many-body theory for a long time to... 

Photoelectron spectroscopy (PES) has been shown to provide a convenient probe of metal ion effective nuclear charge and the nature of the metal-ligand bond via the energy of valence-electron photoionizations (16, 20, 22, 284, 285, 312, 332-334). Recently, PES spectroscopy has been employed in the study of oxo-molybdenum compounds of the type (L-A5)MoE(X,Y) [E = O, S, NO X, Y = halide, alkoxide, or thiolate] in order to evaluate the synergy between the axial (E) and equatorial (X,Y) donors in affecting the ionization energy of the HOMO localized on the Mo center (16, 284, 334). These studies have conclusively shown that equatorial dithiolene coordination electronically bulfers the Mo center in (L-A pMoEttdt) (Fig. 13) from the severe electronic perturbations associated with the enormous variation in the Ji-donor/acceptor properties... 

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). ... 

In addition to transitions in the ir manifold discussed above, some attention has been given recently to possible o-ir states in the ultraviolet nonradlative transitions from the B2jj state. Callomon et al. (27) have postulated the transitions from higher vibrational levels of B2y to a E2u(high resolution absorption spectrum of vapor phase benzene in the 5.0 eV region. initio (12,28) calculations have predicted the presence of at least one a state (e2 ) lying between two filled ir-molecular orbitals. Photoionization (29,30) experiments, and other evidence (31) appear to agree with the conclusion that a-o-ir transition may be... 

Pequignot et al. (2000) discuss two PNe in the Sgr B2 galaxy, He 2-436 and Wray 16-423, whose nuclei are interpreted as belonging to the same evolutionary track. The authors perform a differential analysis of these two PNe, based on tailored photoionization modelling, and argue that while systematic errors may substantially shift the derived abundances, the conclusions based on differences between the two models should not be influenced. The main conclusion is that third dredge up O enrichment is observed in He 2-436, at the 10 % level. 

A kinetic smdy of the shock tube decomposition of CICN led to the conclusion that a set of six reactions are involved in this thermal decomposition (Schofield et al., 1965). Details of the valence shell photoionization of cyanogen halides have been published (Holland and Shaw, 2004), as have the UV absorption spectra of cyanogen halides (King and Richardson, 1966). 

---