Photoionization spectrum

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). 

An excellent agreement with the X-ray photoionization spectra of ethylene, butadiene and hexatriene (7) is obtained (12) (Figure 3) when including in our calculations the Gelius (36) photoionization cross sections for an Alka photon beam, by means of Eqs. (4) and (5). Such a direct comparison is impossible for octatetraene, a compound for which there is no available XPS data. 

Figure 3 Hie simulated ADC[3] X-ray (AlKa) photoionization spectra (full lines) of (a) ethylene, (b) butadiene and (c) hexatriene versus the conesponding experimental records (dotted lines) by MJ. Keane et al... 

Figure 8. Phase lag spectrum of HI in the vicinity of the 5d(n, 8) resonance. In panel (a), the circles show the phase lag between the ionization and dissociation channels. The diamonds and triangles separate the phase lag into contributions from each channel, using H2S ionization as a reference. Panels (b) and (c) show the conventional one-photon (m3) and three-photon (3a>i) photoionization spectra. (Reproduced with permission from Ref. 45, Copyright 2002 American Institute of Physics.)...

Suppose we have two close intermediate states, 2 and 3. In a two-frequency (0)1, 0)2) laser field the atom has two nondistinguishable channels of photoionization. Depending on the phase relationship, the quantum interference of the two channels can be constructive or destructive. In the latter case, the yield of photoionization can be greatly reduced. This effect is related to the well-known Fano resonances in atomic photoionization spectra. Also the interference will generate... 

Figure 11 shows the calculated photoionization spectra in the region of n = 90 for various fields in the range 0.001-2 V/cm. A step size of 10-4 cm-1 was used in the calculations. At 0.001 V/cm (Fig. 1 la) the 92s (sharp) and 90d (broad) Rydberg states appear strongly, and from the linewidths we infer that the lifetimes are approximately 3.8 and 0.2ns, respectively. At 0.1 V/cm the n = 90 manifold appears superimposed on the tail of the 90d resonance. The manifold levels are sharper than the s and d resonances and... 

The best estimates have been obtained to date by using the MINDO and PNDO methods. In Tables 6 to 8 we show the ionization potential values obtained by each of these methods for alkanes and cycloalkanes, alkenes, acetylenes and aromatic compounds. Dewar and Klopman (PNDO) and Dewar et al. (MINDO/2) also compared their calculated inner orbital energies with experimental ionization potentials obtained from photoionization spectra. The ionization potentials of methane and ethane have also been calculated by the PNDO method along the more sophisticated procedure of minimizing separately the energy of the ion and that of the molecule. In these cases, the experimental value of the first ionization potential was reproduced accurately 48>. 

A weakly bound electron submitted to an intense pulse of IR radiation can be ionized by a variety of mechanisms, from multiphoton absorption to tunnel or even over the barrier ionization, depending of the intensity regime, [16]. At higher intensities tunnel ionization and over the barrier processes are dominant and, as a consequence, the ejected electrons are initially relatively slow. This implies that the changes induced by relativity in the corresponding photoionization spectra are expected to be small. 

J.-Z. Tang, I. Shimamura, Mechanism of the enhancement of some high-lying resonance series in the photoionization spectra of excited helium, Phys. Rev. A 50 (1994) 1321. 

To date, since the photoelectron spectroscopy of doped fullerenes has been difficult to perform, numerous theoretical studies of photoionization spectra of atoms encaged in doped fullerenes, performed at various levels of approximations, [15-46], have been prevalent. Consequently, to aid emerging experiments and new theories on gas phase doped fullerenes, a review of the theoretical findings and predictions that have been accumulated in this area of research so far is very timely. This is precisely the aim of the present paper. 

The above discussion was focused on confinement resonances, whether regular or Coulomb, in the photoionization spectra of atoms encaged in a neutral or charged C60 carbon cage. 

Relativistic effects in photoionization of atoms encaged in C60/ A Cso, have fallen under theoretical scrutiny in [29,30], where the photoionization spectra of valence ns subshells in encaged alkaline-earth-metal atoms ( Mg, Ca, Sr and Ba) were detailed. The corresponding key results of [29,30] are highlighted in this section. 

The present paper has focused on novel systems, doped fullerenes, with the emphasis on their photoionization spectra. While the photoionization problem of gas phase doped fullerenes has been experimentally addressed only recently in pioneering works [12,13], there has been much more activity on the theoretical side of the problem this has far outstripped experiment. In the present paper, only those results obtained on the basis of simple semiem-pirical models, the A-potential [15,20-22,27-33,43,44] and 5-potential [34-41] models have been highlighted. Surprisingly, even within the framework of these simple models a rich variety of novel effects, particularly the confinement resonances and their manifestations in the photoionization spectra of doped fullerenes has been unraveled. Although the approximations made are indisputably reasonable for trusting the existence of, and trends in, the predicted confinement resonances, and thereby urging their experimental... 

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... 

An examination of the photoelectron (PE) spectra of 42 five-membered heteroaromatics and simple derivatives thereof, including furan and furan derivatives, showed only minor perturbations of the aromatic structures by the substituents <1993MI811>. Threshold PE spectra as well as photoabsorption and photoion spectra of furan and furan-, 4 have been measured and interpreted <1998CPH(236)365, 2001CPH(263)149>. 

As a consequence of the significance of the XPS in the investigation of the electronic stmcture of molecules and solids, the theoretical model calculations of photoionization spectra became an important area of quantum chemistry [30-35]. One possible way of description of the photoionization process is the perturbation theory. The description of the model would exceed the limits of this paper, so we refer to the textbook of Fulde [36] for the details of the formalism and the applied terminology. In this model the excitations are given by the poles of the Green s matrix Gw(w), i- e. by... 

In sunutary, we have used prototype studies on N2 to convey the progress made in the study of shape resonances in molecular fields, particularly in molecular photoionization. This Included the identification of shape resonant features in photoionization spectra of molecules and the accrual of substantial physical insight into their properties, many of which are peculiar to molecular fields. 

To our knowledge, 46 has never been observed in solution under stable conditions, even at low temperature. Pulse radiolysis " of benzyl chloride as well as flash photolysis ° of several derivatives in HHP have allowed the observation of the electronic absorption spectra of benzyl and its 4-methyl and 4-methoxy derivatives. The and NMR spectra of the 2,4,6-trimethylbenzyl cation and other more heavily substituted benzyl cations, however, have been studied at low temperature in superacid media. In the gas phase, cold benzyl radical has been probed by two-color, resonant two-photon ionization techniques, thus providing very accurate vibrational frequencies below 650 cm for the benzyl cation. Furthermore, the adiabatic ionization energy of benzyl radical and several isotopomers in the ground state were determined from their threshold photoionization spectra using resonant two-photon excitation and detection of electrons by pulsed field ionization. This information, combined with Af//° (CgH5CH2) from Ref. 212 leads to the value of Af//°m(46) reported in Table 9. 

A crucial expoimental result concerning the shapes of SiN was obtained by Jarrold et al. [31]. Investigating the mobilities of size-selected SIn cluster ions in a helium atmosphere the authors conclude that the SIn geometries undergo a transition around N=27 from prolate to quasi-spherical shapes. Photoionization spectra [32] reveal similar features for the clusters in the size range 18 < N < 41, hinting at the possibility of a common bonding network for mid-sized SiN clusters. 

An important characteristic of shape resonances is that they cause non-Franck-Condon effects in vibrationally resolved photoionization spectra. These effects are a consequence of the strong R-variation of the transition moment caused by the R-dependence of the form of the continuum molecular orbital. 

Double photoionization spectra from TPEsCO are simple one-axis graphs, but complete data sets from double photoionization are inherently three-dimensional intensity as a function of two electron energies. Presentation is in the form of two-axis maps, with grayscale or color points to indicate intensity, or by projection into normal spectra of intensity against a single variable. Many choices of axes are possible, and different authors prefer... 

The relative intensity of the 5s l5p l ionization compared with 5p 2 ionization is about 1/20, at both wavelengths. Within the groups of lines of the p4 configuration the relative intensities in complete photoionization spectra seem to agree roughly with the statistical weights of 5 3 1 5 1 for 3P2,i,o> XD2, and S0, with minor deviations. The relative contributions of direct and indirect photoionization can sometimes be separated [65], and where this is done the continuum (direct) part approximately follows the statistical weights at the... 

TABLE I References to Double Photoionization Spectra of Molecules... 

Fig. 3. Comparison of (single-colour) ATI spectra (thin lines) obtained with a Ti sapphire laser with two-colour photoionization spectra (thick lines) in the presence of the 13th harmonic of the laser freouency (/// = 3.0 10 W/cm. ). (a) 1 = 1.0 10 W/cn (b) li = 2.0 10 W/cm. ...

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