| 1. |
- Bolognesi, P., et al.
(författare)
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Inner shell excitation, ionization and fragmentation of pyrimidine
- 2010
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 212, s. 012002-
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Tidskriftsartikel (refereegranskat)abstract
- The inner shell excitation and ionisation of pyrimidine have been studied at the carbon K edge by near-edge X ray absorption fine structure (NEXAFS) and X ray photoelectron (XPS) spectroscopies. The theoretical predictions of density functional theory (DFT) provide a satisfactory assignment of the complex spectra of this polyatomic molecule. The fragmentation following the C(1s -1)π* excitation has been investigated by resonant Auger electron-ion coincidence spectroscopy, which allows a site and state selective study.
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| 2. |
- Couto, Rafael Carvalho, et al.
(författare)
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Breaking inversion symmetry by protonation : Experimental and theoretical NEXAFS study of the diazynium ion, N2H
- 2021
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 23:32, s. 17166-17176
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Tidskriftsartikel (refereegranskat)abstract
- As an example of symmetry breaking in NEXAFS spectra of protonated species we present a high resolution NEXAFS spectrum of protonated dinitrogen, the diazynium ion N2H+. By ab initio calculations we show that the spectrum consists of a superposition of two nitrogen 1s absorption spectra, each including a π∗ band, and a nitrogen 1s to H+ charge transfer band followed by a weak irregular progression of high energy excitations. Calculations also show that, as an effect of symmetry breaking by protonation, the π∗ transitions are separated by 0.23 eV, only slightly exceeding the difference in the corresponding dark (symmetry forbidden) and bright (symmetry allowed) core excitations of neutral N2. By DFT and calculations and vibrational analysis, the complex π∗ excitation band of N2H+ is understood as due to the superposition of the significantly different vibrational progressions of excitations from terminal and central nitrogen atoms, both leading to bent final state geometries. We also show computationally that the electronic structure of the charge transfer excitation smoothly depends on the nitrogen-proton distance and that there is a clear extension of the spectra going from infinity to close nitrogen-proton distance where fine structures show some, although not fully detailed, similarities. An interesting feature of partial localization of the nitrogen core orbitals, with a strong, non-monotonous, variation with nitrogen-proton distance could be highlighted. Specific effects could be unraveled when comparing molecular cation NEXAFS spectra, as represented by recently recorded spectra of N2+ and CO+, and spectra of protonated molecules as represented here by the N2H+ ion. Both types containing rich physical effects not represented in NEXAFS of neutral molecules because of the positive charge, whereas protonation also breaks the symmetry. The effect of the protonation on dinitrogen can be separated in charge, which extends the high-energy part of the spectrum, and symmetry-breaking, which is most clearly seen in the low-energy π∗ transition.
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| 3. |
- Lindblad, R., et al.
(författare)
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X-Ray Absorption Spectrum of the N-2(+) Molecular Ion
- 2020
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 124:20
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Tidskriftsartikel (refereegranskat)abstract
- The x-ray absorption spectrum of N-2(+) in the K-edge region has been measured by irradiation of ions stored in a cryogenic radio frequency ion trap with synchrotron radiation. We interpret the experimental results with the help of restricted active space multiconfiguration theory. Spectroscopic constants of the l sigma(-1 2)(u)Sigma(+)(u) state, and the two 1 sigma(-1)(u) 3 sigma(-1)(g) 1 pi(y) (II alpha)-I-2 states are determined from the measurements. The charge of the ground state together with spin coupling involving several open shells give rise to double excitations and configuration mixing, and a complete breakdown of the orbital picture for higher lying core-excited states.
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| 4. |
- Alagia, M., et al.
(författare)
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Probing the potential energy surface by highresolution x-ray absorption spectroscopy : The umbrella motion of the coreexcited CH3 free radical
- 2007
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Ingår i: Physical Review. A. - 1050-2947 .- 1094-1622. ; 76:2, s. 124305-
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Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the umbrellalike vibration in inner-shell spectroscopy is presented. The high-resolution x-ray absorption spectrum for the lowest lying core excitation of the CH3 free radical was recorded. High quality potential energy surfaces (PES) for the initial and final states of the transition were calculated as a function of the symmetrical stretching and the umbrella deformation coordinates. The strong anharmonicity along the umbrella coordinate in the double-well region of the PES of the core excited state has a strong effect on the bending vibrational progressions. The excellent agreement between the experiment and theory allows an accurate spectroscopic characterization of the vibrational structure of the electronic transition, and the estimation of the umbrella inversion time of 149 fs.
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| 5. |
- Andersson, Egil, 1981-, et al.
(författare)
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Core-valence double photoionization of the CS2 molecule
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:9, s. 94305-
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Tidskriftsartikel (refereegranskat)abstract
- Double photoionization spectra of the CS2 molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h nu=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2 pi(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C 1s)(-1)(2 pi(g))(-1) double vacancy. (C-) 2010 American Institute of Physics. [doi: 10.1063/1.3469812]
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| 6. |
- Carravetta, V., et al.
(författare)
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A screened static-exchange potential for core electron excitations
- 2001
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Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 263:03-feb, s. 231-242
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Tidskriftsartikel (refereegranskat)abstract
- We explore the use of a screened potential for static exchange calculations of core electron excitations, and to which extent this potential can relieve the main limitation of the static exchange method, namely the non-account of the residual screening in the presence of the excited electron. The screened potential is obtained by projecting the target state on a set of polarized orbitals, giving origin to a fully screened potential. Applications are presented and discussed for X-ray absorption spectra of a set of molecules of different size and type. It is found that with the little extra computational effort using the screened potential, the low-energy part of the spectra is generally improved, while the error in the term values are roughly of equal magnitude but of different sign compared to the normal static-exchange calculation. Various aspects of the screened and un-screened static-exchange approximations are analyzed in comparison with other techniques.
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| 7. |
- Carravetta, V., et al.
(författare)
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Ab initio calculations of molecular resonant photoemission spectra
- 2000
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 113:18, s. 7790-7798
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Tidskriftsartikel (refereegranskat)abstract
- An ab initio method for calculations of molecular resonant photoemission (RPE) spectra is described. The method includes a multicenter expansion of both the dipole matrix element-direct emission-and the Hamiltonian matrix element between the resonant state and the autoionizing states-resonant emission. These quantities are relevant for the description of the process both in the two-step model, where the spectrum is computed at the resonance energy only, and in the one-step model where, by a K-matrix approach, the direct-to-resonant interference is taken into account and the electronic line profile is fully described. The resonant two-electron matrix elements are evaluated over the core-excited relaxed orbitals with the outgoing Auger electron orbital expanded on an augmented multicentered Gaussian basis set. Stieltjes imaging is shown to work excellently for such Gaussian basis sets giving correct continuum normalization matrix elements even for RPE electron energies as high as 100-1000 eV. A numerical investigation is carried out for the participator decay of the C 1s --> pi* and O 1s --> pi* states of CO.
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| 8. |
- Carravetta, V., et al.
(författare)
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An ab initio method for computing multi-atom resonant photoemission
- 2002
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 354:02-jan, s. 100-108
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Tidskriftsartikel (refereegranskat)abstract
- We present an ab initio method for computing multi-atom resonant photoemission (MARPE) in molecules and use this method to investigate the possibility of having a sizable MARPE effect. The MARPE cross section is obtained by making multi-center expansions of both the dipole matrix element - direct emission - and the hamiltonian matrix element between the resonant state and the autoionizing states - resonant emission. We show by sample calculations that the resonant contribution exhibits a strong distance dependence of the atoms participating in the MARPE process, and that it is energy dependent and element specific for the neighboring atoms. The ratio of resonant MARPE and direct photoionization cross sections is found to amount to less than one percent which probably makes the molecular MARPE effect difficult to apply in practice.
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| 9. |
- Carravetta, V., et al.
(författare)
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Computational X-Ray Spectroscopy
- 2011
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Ingår i: Computational Strategies for Spectroscopy. - Hoboken, NJ, USA : John Wiley & Sons. - 9780470470176 ; , s. 137-205
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Carravetta, V, et al.
(författare)
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Excitation-energy-dependent resonant photoemission: C1s-pi* spectra of carbon monoxide
- 1997
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Ingår i: PHYSICAL REVIEW A. - : AMER INST PHYSICS. - 1050-2947. ; 56:6, s. 4665-4674
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- High-resolution measurements of the x-ray resonant photoemission of CO near the C1s-->pi* transition are presented. The branching ratios for the valence shell ionization close to the resonance how a strong dependence on the photon energy with a clear asym
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| 11. |
- Carravetta, V., et al.
(författare)
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PH-dependent X-ray Photoelectron Chemical Shifts and Surface Distribution of Cysteine in Aqueous Solution
- 2019
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 123:17, s. 3776-3785
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Tidskriftsartikel (refereegranskat)abstract
- The distribution and protonation states of amino acids in water droplets are of considerable concern in studies on the formation of clouds in the atmosphere as well as in many biological contexts. In the present work we use the amino acid cysteine as a prototypical example and explore the protonation states of this molecule in aqueous solution, which are strongly affected by the acidity of the environment and also can show different distributions between surface and bulk. We use a combination of X-ray photoelectron chemical shift measurements, density functional theory calculations of the shifts, and reactive force field molecular dynamics simulations of the underlying structural dynamics. We explore how the photoelectron spectra distinctly reflect the different protonation states that are generated by variation of the solution acidity and how the distribution of these protonation states can differ between bulk and surface regions. At specific pH values, we find that the distribution of the cysteine species at the surface is quite different from that in bulk, in particular, for the appearance in the surface region of species which do not exist in bulk. Some ramifications of this finding are discussed.
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| 12. |
- Carravetta, V., et al.
(författare)
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Symmetry Breaking and Hole Localization in Multiple Core Electron Ionization
- 2013
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 117:31, s. 6798-6802
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by recent opportunitites to study hollow molecules with multiple core holes offered by X-ray free electron lasers, we revisit the core-hole localization and symmetry breaking problem, now studying ionization of more than one core electron. It is shown, using a N-2 molecule with one, two, three, and four core holes, for example, that in a multiconfigurational determination of the core ionization potentials employing a molecular point group with broken inversion symmetry, one particular configuration is sufficient to account for the symmetry breaking relaxation energy in an independent particle approximation in the case of one or three holes, whereas the choice of point group symmetry is unessential for two and four holes. The relaxation energy follows a quadratic dependence on the number of holes in both representations.
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| 13. |
- Carravetta, V, et al.
(författare)
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X-ray absorption of molecular cations-a new challenge for electronic structure theory
- 2022
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 34:36, s. 363002-
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Forskningsöversikt (refereegranskat)abstract
- In this paper we put forward some historical notes on the development of computational chemistry toward applications of x-ray spectroscopies. We highlight some of the important contributions by Enrico Clementi as method and program developer and as a supporter of this branch of computational research. We bring up a modern example based on the very recent experimental development of x-ray absorption of cationic molecules. As we show this spectroscopy poses new challenges for electronic structure theory and the electron correlation problem.
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| 14. |
- Ekström, Ulf, et al.
(författare)
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Relativistic four-component static-exchange approximation for core-excitation processes in molecules
- 2006
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 73:2
-
Tidskriftsartikel (refereegranskat)abstract
- A generalization of the static-exchange approximation for core-electron spectroscopies to the relativistic four-component realm is presented. The initial state is a Kramers restricted Hartree-Fock state and the final state is formed as the configuration-interaction single excited state, based on the average of configurations for (n-1) electrons in n near-degenerate core orbitals for the reference ionic state. It is demonstrated that the static-exchange Hamiltonian can be made real by considering a set of time-reversal symmetric electron excitation operators. The static-exchange Hamiltonian is constructed at a cost that parallels a single Fock matrix construction in a quaternion framework that fully exploits time-reversal and spatial symmetries for the D2h point group and subgroups. The K - and L -edge absorption spectra of H2 S are used to illustrate the methodology. The calculations adopt the Dirac-Coulomb Hamiltonian, but the theory is open ended toward improvements in the electron-electron interaction operator. It is demonstrated that relativistic effects are substantial for the L -edge spectrum of sulfur, and substantial deviations from the statistical 2:1 spin-orbit splitting of the intensity distribution are found. The average ratio in the mixed region is 1.54 at the present level of theory.
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| 15. |
- Ekström, Ulf, et al.
(författare)
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The umbrella motion of core-excited CH3 and CD3 methyl radicals
- 2008
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Ingår i: Journal of Chemical Physics. - College Park, MD United States : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 128:4, s. 044302-1-044302-11
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Tidskriftsartikel (refereegranskat)abstract
- An accurate experimental and theoretical study of the lowest core excitationof CH3 and CD3 methyl radicals is presented. The complexvibrational structure of the lowest band of the x-ray absorptionspectrum (XAS) is due to the large variation of themolecular geometry, which is planar in the ground state andpyramidal in the core-excited state. The XAS spectra of thetwo radicals were recorded at high resolution and assigned bytheoretical simulations of the spectra, taking into account the couplingof symmetrical stretching and symmetrical bending (umbrellalike) deformations of theradicals. An excellent agreement between experimental and theoretical spectral profilesallowed us to accurately characterize the vibrational structure of theelectronic transition. The similarities, as well as the differences, ofthe peculiar vibrational progression observed for the two radicals areexplained by the strong anharmonicity along the umbrella coordinate andby the isotopic variation, leading to a different probing ofthe double-well potential energy surface of the core excited stateduring the nuclear motion.
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| 16. |
- Feifel, R., et al.
(författare)
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X-ray absorption and resonant Auger spectroscopy of O(2) in the vicinity of the O 1s ->sigma* resonance : Experiment and theory
- 2008
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 128:6
-
Tidskriftsartikel (refereegranskat)abstract
- We report on an experimental and theoretical investigation of x-ray absorption and resonant Auger electron spectra of gas phase O(2) recorded in the vicinity of the O 1s ->sigma* excitation region. Our investigation shows that core excitation takes place in a region with multiple crossings of potential energy curves of the excited states. We find a complete breakdown of the diabatic picture for this part of the x-ray absorption spectrum, which allows us to assign an hitherto unexplained fine structure in this spectral region. The experimental Auger data reveal an extended vibrational progression, for the outermost singly ionized X (2)Pi(g) final state, which exhibits strong changes in spectral shape within a short range of photon energy detuning (0 eV>Omega>-0.7 eV). To explain the experimental resonant Auger electron spectra, we use a mixed adiabatic/diabatic picture selecting crossing points according to the strength of the electronic coupling. Reasonable agreement is found between experiment and theory even though the nonadiabatic couplings are neglected. The resonant Auger electron scattering, which is essentially due to decay from dissociative core-excited states, is accompanied by strong lifetime-vibrational and intermediate electronic state interferences as well as an interference with the direct photoionization channel. The overall agreement between the experimental Auger spectra and the calculated spectra supports the mixed diabatic/adiabatic picture.
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| 17. |
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| 18. |
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| 19. |
- Li, Cui, et al.
(författare)
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Theoretical study of para-nitro-aniline adsorption on the Au(111) surface
- 2016
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Ingår i: Surface Science. - : Elsevier. - 0039-6028 .- 1879-2758. ; 649, s. 124-132
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure, bonding properties and dynamics of para-nitro-aniline (PNA) adsorbed on the Au(111) surface for a sub-monolayer coverge have been investigated by density-functional theory (DFT) static calculations and quantum molecular dynamics simulations. Four main adsorption geometries have been identified by DFT energy optimization with the gradient corrected PBE functional and accounting for the role of the van del Waals (vdW) interaction. Quantum dynamics calculations starting from the four different structures have been performed at room temperature to estimate the relative stability of the adsorbates and the presence of barriers for their interconversion. Quantum simulations suggest that the most stable adsorption geometry at room temperature is that of PNA with a slightly distorted molecular plane almost parallel to the Au(111) surface. In a second less populated configuration the PNA molecule interacts with the substrate by its NO2 group while the molecular plane is orthogonal to the surface. The N 1s electron photoemission spectrum has been simulated for the identified adsorbate geometries and a measurable variation of the absolute and relative chemical shift for the two nitrogen atoms in comparison with the known values for PNA in gas phase is predicted.
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| 20. |
- Niskanen, Johannes, et al.
(författare)
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Experimental and theoretical study of core-valence double photoionization of OCS
- 2010
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 82:4, s. 043436-
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Tidskriftsartikel (refereegranskat)abstract
- O 1s, C 1s, and S 2p core-valence double ionization electron spectra of the OCS molecule have been obtained experimentally by a time-of-flight photoelectron-photoelectron coincidence spectroscopy technique. In order to analyze and assign the spectral features observed, we present a protocol for computing core-valence ionization energies of such systems. The protocol is based on a restricted active space multiconfigurational self-consistent field (MCSCF) methodology with a freeze-relax procedure to guarantee a correct core-valence state root index without variational collapse. Corrections for extended dynamical correlation and core-core correlation, respectively, are made by multiconfigurational perturbation theory and by uncontracted basis set Moller-Plesset theory. Envisioning applications to larger molecules, a spin-restricted open-shell density functional method is also applied for the lowest core-valence energies. Furthermore, cross sections through a scheme for computing multiatom Auger transitions generating core-valence holes are presented. We find that the procedure outlined is capable of deriving the energy onset of core-valence ionization within a fraction of an eV and that assignments can be made of the most salient spectral features.
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| 21. |
- Niskanen, Johannes, et al.
(författare)
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Valence photoionization of the LiCl monomer and dimer
- 2010
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 81:4, s. 043401-
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports a study of valence photoionization of the LiCl monomer and dimer. The behavior of the photoionization partial cross section for molecular valence orbitals was measured as a function of photon energy between 15 and 35 eV. A square-integrable-function method was used to model the ionization partial cross section in both the LiCl monomer and dimer.
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| 22. |
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| 23. |
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| 24. |
- Plashkevych, O, et al.
(författare)
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On the validity of the equivalent cores approximation for computing X-ray photoemission and photoabsorption spectral bands
- 2000
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Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 260:1-2, s. 11-28
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Tidskriftsartikel (refereegranskat)abstract
- We evaluate the performance of the equivalent cores (Z + 1) approximation for computing core photoemission and photoabsorption spectral bands versus full self-consistent field optimizations. Franck-Condon factors are obtained using the linear coupling model with the multi-dimensional vibronic coupling constants computed from analytical calculations of the ground state frequencies and normal coordinates, and excited state energy gradients evaluated at the ground state equilibrium geometry. We use carbon monoxide, formaldehyde, chloromethanes and some monosubstituted benzenes for the purpose. Considering other inherent approximations in the calculations, we find that the equivalent core model works well for band shapes and comparatively better for excitations of strong modes and ionization of deeper core levels. The approximation also works somewhat better for photoemission than for discrete photoexcitation.
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| 25. |
- Plashkevych, O., et al.
(författare)
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Vibronic structure fingerprints in NEXAFS : a theoretical study of 2-mercaptobenzoxazole
- 2000
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 327:02-jan, s. 7-12
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Tidskriftsartikel (refereegranskat)abstract
- We use 2-mercaptobenzoxazole to study the notion of vibronic fine structure fingerprints in near-edge X-ray absorption fine structure (NEXAFS). It is shown that connected and non-connected carbons in the phenyl ring of the 2-mercaptobenzoxazole molecule give mutually similar excitation patterns and patterns similar to the one in free benzenewas while the 5-ring carbon is distinctly different in this respect. The simulated vibronic bands give an unambiguous assignment of the full NEXAFS spectrum at the carbon K-edge.
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| 26. |
- Salek, Pawel, et al.
(författare)
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Dynamical suppression of atomic peaks in resonant dissociative photoemission
- 2001
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 343:3-4, s. 332-338
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Tidskriftsartikel (refereegranskat)abstract
- Resonant excitation to the F1s-sigma* dissociative state in hydrogen fluoride gives a photoelectron spectrum where the spectator part contains strong atomic lines but a participator part where such lines are lacking. We demonstrate that this contrasting behaviour between the two parts is due to a strong dynamical suppression of the resonant contribution, making direct main state photoionization the dominating channel even at resonant conditions.
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| 27. |
- Salek, P, et al.
(författare)
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Dynamical suppression of atomic peaks in resonant dissociative photoemission
- 2001
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Ingår i: CHEMICAL PHYSICS LETTERS. - : ELSEVIER SCIENCE BV. - 0009-2614. ; 343:3-4, s. 332-338 Language: English
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant excitation to the F1s-sigma* dissociative state in hydrogen fluoride gives a photoelectron spectrum where the spectator part contains strong atomic lines but a participator part where such lines are lacking. We demonstrate that this contrasting b
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| 28. |
- Salek, Pawel, et al.
(författare)
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Theory and first principles calculations of dissociative resonant photoionization : The evolution of atomic peaks and holes
- 2002
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 116:2, s. 629-645
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Tidskriftsartikel (refereegranskat)abstract
- We present theory and computational method for analyzing dissociative resonant photoemission from first principles. Particular emphasis is devoted to the conditions for observing so-called atomic peaks and atomic holes. The atomic peaks are connected with photoemission following resonant excitation to dissociative core excited states which show signals from scattering channels involving the dissociation (atomic) fragments in addition to those involving the compound molecule. The holes are the results of continuum-continuum interference effects between these two, atomic and molecular, channels which may act destructively under certain conditions. We apply a novel electronic structure method to compute the transition moments for the resonant and direct photoemission channels including their dependence on internuclear distances and their interference. The relevant matrix elements involving the photoelectron are obtained using similar techniques for the two types of channels, with the scattered electron wave in each case being determined in the full molecular anisotropic potential. A study of resonant photoemission through the core excited sigma* states of HF and HCl indicates that the appearance of the atomic peaks and holes is subtly dependent on the nuclear dynamics, the potential energy curves, and the excitation photon frequency. We demonstrate that the resonant contribution and the evolution of the atomic peaks can be subject to strong dynamical suppression, so strong in fact that main state photoionization may constitute the dominating channel even at resonant conditions. It is shown that such dynamical suppression explains that resonant excitation to the F 1s-sigma* dissociative state in hydrogen fluoride gives a photoelectron spectrum in which the spectator part contains strong atomic lines but a participator part where such lines are lacking, although they both refer to the same, dissociative, core excited state. The findings in the present work give evidence that both direct and resonant channels should be simultaneously considered in analyses of the dissociative photoemission process even at resonant conditions.
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| 29. |
- Sorensen, S. L., et al.
(författare)
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Electronic Doppler effect in resonant Auger decay of CO molecules upon excitation near a shake-up Pi resonance
- 2007
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : APS. - 1050-2947 .- 1094-1622. ; 76:062704
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Tidskriftsartikel (refereegranskat)abstract
- Wepresent an experimental observation of the electronic Doppler effect inresonant Auger spectra upon core excitation slightly above the carbonK edge of the CO molecule. Thus the electronic Dopplereffect has been identified in above-threshold excitation, and in atransition of symmetry. Ab initio calculations of the potentialenergy curves of the relevant states of CO and thewave packet technique have been employed to provide a theoreticalbackground to the experimental studies. The weak feature around 299.4 eVin the photoabsorption spectrum, whose decay has been investigated bythe present experiment, is assigned to double (core-valence) excitations toC 1s shake-up states |1s1−1*2 with a strong dissociative character,and the Doppler splitting of the atomic peak has beenreproduced by the simulation.
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| 30. |
- Yang, L, et al.
(författare)
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Energy-dependent valence photoelectron spectra of SF6. Ab initio calculations and measurements
- 1998
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Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. - 0368-2048. ; 94:1-2, s. 163-179
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Ab initio calculations of branching ratios and cross-sections for inner- and outer-valence levels of SF6 have been carried out by means of the static exchange (STEX) approximation including full intrachannel interaction. The calculations cover an energy r
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