[Show abstract][Hide abstract] ABSTRACT: Ozone is found to exhibit substantial site-selective fragmentation when its fragment ions are collected in coincidence with energy selected electrons. We find a preferential production of the Oþ2 =OþðOþ=OþÞ ion pair upon ionization of the terminal (central) oxygen 1s electron. Depending on the hole localization, Auger rates are different towards the various final states of the dication, which would produce the observed different fragmentation pattern. We also observe however an increase Oþ2 =Oþ production for when the terminal core-hole state is vibrationally excited. This shows the role of the nuclear motion before the Auger decay in the observed site-specific.
Full-text · Article · Jun 2007 · Chemical Physics Letters
[Show abstract][Hide abstract] ABSTRACT: The below-threshold region in core-excited O2 is very complex, consisting of a multitude of exchange-split states with mixed molecular orbital-Rydberg character. We have investigated the nature of these intermediate states by resonant Auger spectroscopy. In particular, we have obtained constant-atomic-final-state yield curves for several atomic peaks in the electron decay spectra which are stemming from ultrafast dissociation. The relative intensity of Auger decay leading to atomic final states is considered a signature of the relative weight of the sigma* character. This method allows one to "filter out" intermediate states with dissociative character. Extensive calculations have been performed by multi-reference configuration interaction at different interatomic distances in order to evaluate the potential curves of the core-excited states and propose a qualitative description of the dissociative molecular dynamics. The calculations show that the core-excited states have a relevant admixture of excitations to orbitals with Rydberg character and excitations to the sigma* orbital with different spin couplings. A diabatization of the adiabatic potential curves shows that the coupling between Rydberg and sigma* diabatic states is very different at the different crossing points and ultrafast dissociation occurs more easily on the lowest sigma* diabatic potential curve. As a consequence, the observation of atomic peaks only in the lower-energy region of the absorption curve is well justified.
No preview · Article · Sep 2005 · The Journal of Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: Core excitation from terminal oxygen OT in O3 is shown to be an excitation from a localized core orbital to a localized valence orbital. The valence orbital is localized to one of the two equivalent chemical bonds. We experimentally demonstrate this with the Auger-Doppler effect which is observable when O3 is core excited to the highly dissociative OT1s(-1)7a1 1 state. Auger electrons emitted from the atomic oxygen fragment carry information about the molecular orientation relative to the electromagnetic-field vector at the moment of excitation. The data together with analytical functions for the electron-peak profiles give clear evidence that the preferred molecular orientation for excitation only depends on the orientation of one bond, not on the total molecular orientation. The localization of the valence orbital "7a1" is caused by mixing of the valence orbital "5b2" through vibronic coupling of antisymmetric stretching mode with b2 symmetry. To the best of our knowledge, it is the first discussion of the localization of a core excitation of O3. This result explains the success of the widely used assumption of localized core excitation in adsorbates and large molecules.
Full-text · Article · May 2005 · The Journal of Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: Sweden, together with the other Nordic countries, seems at first glance to offer an environment where women and men enjoy equal treatment at all levels of society. Governments proclaim policies invoking gender-neutral regulations and legal frameworks. Government-supported parental leave programs provide paid leave for both parents, the child-care system is well developed, women are represented at high levels in the government, and educational levels are high. Clearly, awareness of gender issues and openness in the classroom and workplace must be very high. Why, then, is the career pipeline for women in physics leaking so badly? Why are there so few women in high-level management positions in industry? How can salaries for women on all levels, not least within the public sector, be consistently lower than for their male counterparts? What factors are important and how can we influence the situation so that women receive their fair share of power and recognition for their achievements? We discuss some of these issues, and describe the present situation in Sweden.
[Show abstract][Hide abstract] ABSTRACT: An in-depth photoionization study of the inner-valence electrons in HCl and DCl has been performed using synchrotron radiation. A series of photoelectron spectra of HCl were obtained at a resolution of 23 meV over the binding energy range 25-30.5 eV at various excitation energies and at two different electron collection angles relative to the plane of polarization of the undulator radiation. In addition, photoelectron spectra of DCl were recorded at two different excitation energies. These spectra were compared directly with the threshold photoelectron spectra of HCl and DCl that were recorded previously under similar resolution conditions (~30 meV). This comparative study reveals new information on the nature of the numerous band systems observed in this binding energy region. In addition, we present the experimental confirmation of the theoretical prediction given by Andersson et al (2001 Phys. Rev. A 65 012705) that a vibrational progression showing interference structure would appear in the main inner-valence ionization band in the photoelectron spectrum of DCl at a resolution of 10 meV.
Full-text · Article · Mar 2004 · Journal of Physics B Atomic Molecular and Optical Physics
[Show abstract][Hide abstract] ABSTRACT: Resonant Auger electron spectra of core excited O3 (OT1s−12b11) are presented for the first time. The photoionization valence spectrum with sample purity and resolution superior to those published is presented. The first direct experimental evidence for the C̃2 B1 state of O3+ is found. Ab initio calculations of the resonant Auger electron (RAE) spectrum have been performed supporting the assignment of the C̃-state.
Full-text · Article · Jun 2003 · Chemical Physics Letters
[Show abstract][Hide abstract] ABSTRACT: We present multicoincidence spectra of nitrogen, formic acid and methyl methacrylate. We demonstrate how to probe the local symmetry of molecular orbitals from molecules core excited with linearly polarized synchrotron radiation. The intensity distribution of the photoelectron photo-ion photo-ion coincidence (PEPIPICO) spectrum reflects the selectivity and localization of core excitation by polarized light. By simulating the spectra the angular dependence of the fragmentation is determined.
[Show abstract][Hide abstract] ABSTRACT: High-resolution, angle-resolved resonant Auger electron spectra of the NO molecule in the regions of both N and O 1s→2π core electron excitations are presented. A large number of vibrational final states are resolved due to high energy resolution. Calculations based on lifetime vibrational interference (LVI) theory neglecting interference between different electronic intermediate states and between direct and resonant channels have been performed. A comparison between theoretical and experimental spectra shows that LVI theory describes the major spectroscopic features quite well. The same holds for the evolution of the angular averaged partial cross sections with the change of excitation energy. The angular distribution of particular vibrational final states are, however, not described successfully with LVI calculations at the present level of sophistication. A theoretical analysis supports that one reason for this deviation is electronic state interference.
[Show abstract][Hide abstract] ABSTRACT: We present evidence for ultra-fast dissociation of molecular ammonia when photo-excited to the N1s→4a1 core-hole state. This finding is based on resonant Auger spectroscopical results as well as qualitative arguments concerning the photon energy dependence of the Auger structures. Calculations of the excited state potential based on the Z+1 approximation were performed. Both the calculations and the measurements indicate that the most likely fragmentation pathway for the core excited ammonia molecules leads to NH2* and H fragments.
Full-text · Article · Mar 2003 · Chemical Physics Letters
[Show abstract][Hide abstract] ABSTRACT: The silicon 2p photoelectron spectra for SiH4, SiF4, and SiCl4 have been analyzed to give the natural linewidths of the Si 2p hole states, which reflect the Auger decay rates of the states. For SiH4 the measured width of 38 meV is in approximate agreement with the prediction of the one-center model (32 meV), but that for SiF4 of 79 meV is more than 5 times the value of 14 meV predicted by this model. Approximate theoretical calculations indicate that valence electrons from the fluorine atoms of SiF4 play an important role in the Auger decay via interatomic processes.
Full-text · Article · Dec 2002 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: Vibrationally resolved C1s photoelectron spectra of benzene and d6-benzene have been recorded using monochromated synchrotron radiation at photon energies of 330 eV. The spectrum of normal benzene displays considerable vibrational structure. Particularly noteworthy is the strong excitation of a combined CCH-bending and CC-stretching mode which splits the main peak into two well-defined maxima. In d6-benzene, the vibrational energy levels are less well separated and the vibrational structure is reduced to strong asymmetry of the main peak and a broad tail extending toward higher ionization energy. The recorded spectra are analyzed using first-principle and curve-fitting procedures. A theoretical model that allows for incomplete localization of the core hole, results in very good fits to the experimental spectra of both benzene and d6-benzene.
Full-text · Article · Nov 2002 · Physical Chemistry Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: In the xenon N4,5OO Auger spectrum there are 19 prominent lines ranging in kinetic energy from 8 to 36 eV that provide a convenient set of standards for calibrating electron spectrometers. Combining optical data with recent measurements of this spectrum gives energies for these lines that are absolutely accurate to 11 meV. For most lines the relative accuracy is better than 1 meV; for a few it is about 3 meV. The spin–orbit splitting of the xenon 4d lines is determined to be 1979.0±0.5 meV.
Full-text · Article · Aug 2002 · Journal of Electron Spectroscopy and Related Phenomena
[Show abstract][Hide abstract] ABSTRACT: Trends in carbon 1s ionization energies for the linear alkanes have been investigated using third-generation synchrotron radiation. The study comprises CH(4), C(2)H(6), C(3)H(8), C(4)H(10), C(5)H(12), C(6)H(14), and C(8)H(18). Both inter- and intramolecular shifts in ionization energy have been determined from gas-phase spectra and ab initio calculations. The shifts are decomposed into initial-state and final-state contributions and are shown to relate to the fundamental chemical properties of group electronegativity and polarizability. By extrapolation, we predict C1s spectra of larger n-alkanes, converging toward isolated strands of polyethylene.
No preview · Article · Aug 2002 · Journal of the American Chemical Society
[Show abstract][Hide abstract] ABSTRACT: We report an experimental investigation of higher vibrational levels (ν′>2) of the C 1s⃗π* excitation in CO utilizing resonant Auger electron spectroscopy. These vibrational states are not readily seen in a total yield absorption spectrum, whereas they are shown to be discernable in a partial electron yield spectrum. Furthermore, the nature of the spectator part between EBin=26.5 and 30 eV, being subject of an ongoing debate, is discussed on the grounds of the presented experimental data. The experiments indicate that the formally used adiabatic framework for the multitude of close lying 2Π potential curves is inappropriate, but that a diabatic treatment can be used for the interpretation of the spectra.
Full-text · Article · Jun 2002 · Physical Review A
[Show abstract][Hide abstract] ABSTRACT: The Auger–Doppler effect in the experimental spectra of HF and DF is presented, and the dynamics of ultra-fast dissociation in the core-excited state are discussed. The Doppler splitting of the atomic Auger peak is calculated and simulated using a classical model and a very good agreement is found between experiment and simulation. It is shown that the difference in photon energy relative to the resonance is transferred completely into the kinetic energy release (KER). This is expected to be a general phenomenon, but is clearly illuminated in the HF/DF case. Thus the fragment velocity can be controlled through photon energy detuning.
Full-text · Article · Mar 2002 · Chemical Physics Letters
[Show abstract][Hide abstract] ABSTRACT: Vibrational structures of the C1s and N1s photoelectron spectra of gas-phase HCN have been investigated using monochromated third-generation synchrotron radiation. Both spectra exhibit resolved fine structure associated with several vibrationally excited states. In the C1s spectrum a single vibrational progression is observed, while the N1s spectrum is more complex. High-level ab initio calculations were performed to simulate the spectra and the agreement with the experimental results is good. Based on the calculations, the C1s ionisation is found to induce vibrations solely in the C≡N stretching mode with an energy of 280 meV, while the N1s ionisation generates vibrations also in the C-H stretching mode with an energy of about 387 meV, as well as combinations of these two modes.
[Show abstract][Hide abstract] ABSTRACT: We report the experimental observation of a strongly selective population of the spin-orbit components in the HCl+ X~2ΠΩ states after excitation into the dissociative 2p-16σ* core excited state. A progression of highly excited vibrational states with either the Ω=3/2 or Ω=1/2 component of the final state is populated, respectively, when the excitation is tuned in the 2p-13/26σ* or 2p-11/26σ* part of the resonance. This effect is explained theoretically to be due to the orientational selectivity of the excitation process and the preference of the L2,3VV Auger process to produce valence holes with the same
orientation as the core holes.
Full-text · Article · Feb 2002 · Physical Review A
[Show abstract][Hide abstract] ABSTRACT: In the xenon N4,5OO Auger spectrum there are 19 prominent lines ranging from 8 to 36 eV that provide a convenient set of standards for calibrating electron spectrometers. Combining optical data with recent measurements of this spectrum gives energies for these lines that are absolutely accurate to 11 meV. For most lines the relative accuracy is better than 1 meV; for a few it is about 3 meV. The spin-orbit splitting of the xenon 4d lines is measured to be 1979.0 +- 0.5meV.
Full-text · Article · Feb 2002 · Journal of Electron Spectroscopy and Related Phenomena
[Show abstract][Hide abstract] ABSTRACT: The resonant photoemission of HCl through an autoionizing resonance to the spin-orbit split X̃2π1/2 and X̃2π3/2 final states of HCl+ was investigated. It was found that resonant photoemission via the dissociative Cl 2p-16σ core-excited state causes a pronounced (>9%) selectivity of either one or the other spin-orbit component depending on whether the excitation is tuned to the 2p3/2-16σ or 2p1/2-16σ component of the resonance. This paper investigates the origin of this selectivity and discusses the implications of this phenomenon.
[Show abstract][Hide abstract] ABSTRACT: The HCl inner-valence photoelectron band at 26 eV binding energy has been recorded at high resolution. Discrete peaks arising from at least two separate vibrational progressions are superimposed on the broad continuum. Fano profiles are visible in one of the progressions. This indicates interference between superimposed electronic states, where weak avoided crossing allows two adiabatic states to couple. In the isotopic DCl molecular spectrum, the discrete lines are less pronounced, due to slower dissociation and therefore less coupling between the continuum and the bound state.
Full-text · Article · Dec 2001 · Physical Review A