Final state correlation effects on the auger transition rates of methane

The doubly ionized Auger final states of CH₄ and the corresponding states of of Ne atom are studied by semi-internal configuration interaction (Cl) calculations. Correlation redistributes dramatically the intensities between the Auger diagram states and gives rise to strong satellite peaks in the law-kinetic-energy part of the spectrum.     

New correlation effects in the photoionization of atoms and ions

Recent advances in experimental and computational capabilities have provided the impetus for highly detailed studies of the photoionization process in atoms and ions. As a result, there have been a number of new phenomena uncovered. And these new phenomena are, in a general sense, of correlation among the atomic electrons, i.e., the breakdown of the single-particle approximation. Of particular interest are cases where correlation is not merely a small perturbation on the single-particle model, but where correlation dominates the process. In this paper, a number of illustrative experimental and theoretical examples are presented in which electron–electron correlation is seen to be a primary determinant of the process.     

Interchannel coupling effects on non-dipole photoionization parameters

Interchannel coupling effects involving non-dipole matrix elements on photoelectron angular distribution have been recently found to be of significant importance even at energies not so high above ionization thresholds. Studies have been reported on the angular distribution of photoelectrons from some inert gas atoms: Ne, Ar, Kr and Xe. In the present work, we report further studies on atomic xenon, and also results on atomic mercury, using the relativistic random phase approximation. Also, we report the angular distribution asymmetry parameters with the inclusion of non-dipole terms for a confined atom; @ Ca is considered as a model system for this study.     

Electric field effects in the photoionization and photoabsorption of methyl iodide

The effects of relatively high static electric fields (133–6533 V/cm) in the photoionization and photoabsorption of methyl iodide below the first and second ionization limits are reported. As opposed to the minor effect of the field in the photoabsorption, significant changes are observed in the photoionization below the thresholds. The changes induced by the field in the photoionization signal are explained in terms of a simple model based on the absorption spectra and on the photoionization spectrum recorded with the lowest applied field.     

Vibrationally resolved photoionization dynamics of CF4 in the D 2A1 state

Vibrationally resolved photoelectron spectroscopy of the CF4+ (D 2A1) state is studied for the first time over an extended energy range, 26.5相似文献   

Final charge state distribution in the production and decay of hollow Ar

The improved model of radiative-Auger-cascade with shake-off effect is applied to calculate the final charge state distribution and the X-ray and Auger electron spectra emitted during the cascade decay of Ar, with the initial 1s hole created by the synchrotron irradiation. The discrepancy in the predicted charge distribution without the shake-off effect is removed. It was found that the discrepancy was caused mainly by the neglect of the shake-off effect during the productin stage of the 1s hole, and not by the shake-off effect during the decay of the 1s hole. The X-ray and Auger spectra predicted by the improved model are compared with that without the shake-off. The charge distributions resulting from a 2s or 2p initial hole are also presented.     

Electron-spin polarization of photoions produced through photoionization from the laser-excited triplet state of Sr

We report the detailed experimental study on the production of electron-spin-polarized Sr+ ions through one-photon resonant two-photon ionization via laser-excited 5s5p 3P1 (MJ = +1) of Sr atoms produced by laser-ablation. We have experimentally confirmed that the use of laser-ablation for the production of Sr atoms prior to photoionization does not affect the electron-spin polarization. We have found that the degree of electron-spin polarization is 64+/-9%, which is in good agreement with our recent theoretical prediction. As we discuss in detail, we infer, from a simple analysis, that photoelectrons, being the counterpart of electron-spin-polarized Sr+ ions, have approximately the same degree of electron-spin polarization. Our experimental results demonstrate that the combined use of laser-ablation technique and pulsed lasers for photoionization would be a compact and effective way to realize a pulsed source for spin-polarized ions and electrons for the studies of various spin-dependent dynamics in chemical physics.     

Functional group effects in laser-excited multi-photon photoionization of organics in liquid solutions

Of the organic compounds examined for possible two-photon photoionization behavior, 43% were found to yield analytically useful photoionization with excitation at 308 nm. Fifty-five per cent produced greater photoionization responses than aniline, the de facto photoionization standard. Additionally, 16 of the surveyed compounds were more photoionization efficient (i.e., exhibit higher photoionization per unit absorption cross-section) than aniline. It was found that photoionization is relatively easily achieved with primary amines, anilines and diamines. Less readily photoionized were primary and tertiary amides, esters, alkyl ethers, and most halogenated compounds, the main exceptions being the halogenated anilines. Tertiary amines and fluorinated compounds gave poor photoionization results.     

Many-body effects in molecular photoionization in intense laser fields; time-dependent Hartree-Fock simulations

The time evolution of the reduced single electron density matrix for eight electrons in a one-dimensional finite box potential driven by an intense laser field is calculated by numerically integrating the time-dependent Hartree-Fock equations. We study the effects of the Coulomb interaction, field intensity, and frequency on the time profile of the ionization process. Our computed saturation ionization intensity (Isat) is in good agreement with experimental results for decatetraene [Ivanov et al. J. Chem. Phys. 117, 1575 (2002)].     

Correlation effects in the valence x-ray photoionization spectra of ethylene,butadiene, and hexatriene

The x-ray photoemission spectra of the ethylene, butadiene, and hexatriene compounds were investigated using one-particle Green's function calculations which are exact up to third order in correlation. This study points to the importance of initial-state correlation and cross-section effects for a consistent reproduction of satellite bands recorded under x-ray photoionization. By extrapolating the results obtained to larger unsaturated hydrocarbons, it is clear that the signal recorded in the inner-valence region of polyacetylene must be exclusively assigned to many-body structures. This study also provides evidence for a partial contamination of the outer-valence band by shake-up lines. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 465–481, 1997     

Bonding in a borylene complex investigated by photoionization and dissociative photoionization

The borylene complex [(OC)(5)Cr=B=N(SiMe(3))(2)] has been investigated by using threshold photoelectron-photoion coincidence spectroscopy with synchrotron radiation. The ionization energy of the parent complex and the 0?K appearance energies of the sequential CO loss channels have been determined. The derived bond-dissociation energies are used to discuss bonding and energetics in this compound.     

Dipole operators in photoionization calculations

The photoionization cross section and asymmetry parameter are reported for hydrogen molecule-ion. The calculations were performed using the dipole length and dipole velocity operators in the energy range from threshold to 270 eV photon energy. The results indicate that the calculations are very sensitive to the accuracy of the bound state wavefunction, and that the velocity operator gives more accurate results.     

Shape resonances in the valence-shell photoionization of cyanogen

Vibrationally-resolved photoelectron angular distributions for the first four valence-shell photoionizations of cyanogen have been measured with NeI, HeI and NeII line sources. Calculated photoionization cross sections and asymmetry parameters are reported for photon energies up to 50 eV. The experimental and theoretical results indicate the presence of several shape resonances.     

On the photoionization of large molecules

There is no apparent limit to the size of a molecule for which photoionization can occur. It is argued that it is difficult to obtain useful photoionization mass spectra of peptides (above ～ 2000 u), proteins, and oligonucleotides, because of the high internal energy of these polar molecules as a result of the desorption event and because vibrationally excited radical cations readily fragment. Evidence to support this hypothesis is presented from the 118-nm single-photon ionization (SPI) mass spectra of the cyclic decapeptide gramicidin S and of fullerenes, from null SPI results with the linear peptides substance P and gramicidin D and oligonucleotides, and from a variety of data found in the literature. The literature data include mass spectra from jet-cooled peptides, perfluorinated polyethers, collisional ionization of small neutral peptides, and the ultraviolet photoelectron spectroscopy of polymeric solids.     

The ground state tautomer in the excited state relaxation process of 3-hydroxyflavone at room temperature

Very recently, the ground state reverse proton transfer in 3-hydroxyflavone (3-HF) has been reported to take place within 30 ps by picosecond transient absorption spectroscopy by Aartsma and co-workers. Here we present evidence of intervention of a long-lived ground state tautomer involved in the excited state relaxation process of 3-HF by transient absorption and two-step laser excitation fluorescence spectroscopy.     

A new relaxation process in the high-elastic state at low temperatures

A new relaxation process, explaining the change of elasticity in rubberlike polymers at critical stress (0.1?0.5 kgf/cm²) has been discovered. This process is characterized by the low value of activation energy (weak temperature dependence of relaxation times) and large sizes of kinetic units (strong dependence of relaxation time on stress). Critical stress depend on temperature and for rubberlike polymers turns to zero at 40°?60°C. Mechanism of the phenomena can be explained by the existence of the ordered molecular microregions, creating additional crosslinking points of nonchemical nature with free chains of the network, breaking up at critical stress. Observed phenomena is analogous to the process of forced rubber elasticity of those polymers in glassy state. Critical stress is analogous to the limit of forced rubber elasticity below glass transition temperature.     

Solid state effects in the IR spectrum of octahydridosilasesquioxane

Infrared spectrum of Octahydridosilasesquioxane, in the solid state, is reported and analyzed to show the presence of significant solid state effects. This is in marked contrast with the reported Raman spectroscopic studies of this compound in the solid state where no evidence for such a proliferation of these effects were found. It is found that the normal modes with radial motion of the atoms in their normal coordinate are distinguishable from other vibrations by the distinct correlations between the band intensity and the solid state splitting observed in the IR spectrum. This new insight suggests an interchange of the literature assignments of the two modes nu27 and nu29 in the IR spectrum and a different origin to the doublet of bands in the Raman spectrum at 883 and 897 cm(-1).     

Near-threshold shape resonance in the photoionization of 2-butyne

Photoelectron velocity map imaging is combined with one- and two-photon ionization to study the near threshold photoionization of the 2-butyne molecule. In this region, the photoabsorption and photoionization cross sections display a very intense broad feature that is assigned to an l = 4, π(g) shape resonance. The effect of this shape resonance on the vibrational branching ratios and photoelectron angular distributions is explored. Theoretical calculations of the photoionization cross section and photoelectron angular distributions are in good agreement with the experiments. The results for 2-butyne are compared with those of acetylene, propyne, and 1-butyne, none of which show such significant enhancements near threshold, and the differences are rationalized in terms of the symmetries and orbital angular momenta of the highest occupied orbitals and the corresponding shape resonances. Expectations for larger alkynes and alkynyl radicals are also discussed. A preliminary measurement of the ionization energy of the 2-butyne dimer is also presented.