| 1. |
- Magnuson, Martin, et al.
(författare)
-
Competition between decay and dissociation of core-excited carbonyl sulfide studied by x-ray scattering
- 1999
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 59:6, s. 4281-4287
-
Tidskriftsartikel (refereegranskat)abstract
- We show evidence of dissociation during resonant inelastic soft x-ray scattering Carbon and oxygen K-shell and sulfur L-shell resonant and nonresonant x-ray emission spectra were measured using monochromatic synchrotron radiation for excitation and ionization. After sulfur L-2,L-3-->pi*, sigma* excitation, atomic lines are observed in the emission spectra as a consequence of competition between de-excitation and dissociation. In contrast thr carbon and oxygen spectra show weaker line-shape variations and no atomic Lines. The spectra are compared to results from ab initio calculations. The discussion of the dissociation paths is based on calculated potential energy surfaces and atomic transition energies.
|
|
| 2. |
- Norman, Patrick, 1968-
(författare)
-
Nonlinear Optical Properties of Fullerenes, Oligomers, and Solutions
- 1998
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work presents development and applications of modern tools in ab initio quantum chemistry for obtaining linear and nonlinear response properties of molecules in the gas phase and in solution. The external perturbing fields are primarily electric in nature with frequencies in the optical region.The framework for this achievement is denoted response theory, a formulation of time-dependent perturbation theory, which has been extended to include fourth-order properties fully analytically for self-consistent field (SCF) and multi-configurational SCF (MCSCF) reference states. This extension refers both to the vacuum theory as well as to a self-consistent reaction field model for properties in solution.Applications are presented, displaying both the possibilities and limitations of the theory. Highly electron correlated MCSCF reference states are used for small molecules both in the gas phase and in solution to obtain accurate values of ground and excited state polarizabilities $\alpha$, and ground state hyperpolarizabilities $\beta$ and $\gamma$. Excited state properties are addressed without explicit optimization of the state in question but instead by computing a double residue of the cubic response function. We have in some cases considered both the electronic and the vibrational contributions to these properties. Another direction that has been pursued is to, at the random phase approximation (RPA) level, extend the range of applications for large-scale systems by means of direct atomic orbital driven routines in a parallel scheme. In this context, we address structure-to-property relations for two-dimensional hydrocarbon oligomers, and electron-delocalization of fullerenes. With small we mean molecules with up to 15 atoms and with large-scale we mean molecules with up to 150 atoms.
|
|
| 3. |
- Chotai, Jayanti, 1948-
(författare)
-
Season of birth in suicidology : neurobiological and epidemiological studies
- 1999
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Several neuropsychiatrie disorders have shown season of birth associations. Low cerebrospinal fluid (CSF) levels of the serotonin metabolite 5-HIAA and the dopamine metabolite HVA have been associated with suicidal behaviour, impulsivity, and aggression. This thesis investigated associations between the season of birth, the CSF levels of three monoamine metabolites (including MHPG of norepinephrine), the scales of the diagnostic interview for borderline patients (DIB), and psychiatric diagnoses. Also, the methods of suicide were investigated in relation to the season of birth.Methods: We studied a clinical sample of 241 patients in Stockholm with mood, anxiety and adjustment disorders with respect to the CSF levels of monoamine metabolites in relation to the season of birth, and in relation to the DIB in an overlapping sample. We also analysed all completed suicides during the 42 years 1952- 1993inVästerbottenin northern Sweden (1466 cases) by multiple logistic regressions to relate suicide methods with season of birth, gender, age, urban-rural residence, marital status, year of suicide, and season of suicide. For the 20 years 1961- 1980 (693cases), psychiatric in-patient and out-patient records were also examined for any history of psychiatric contacts and psychiatric diagnoses. In two mutually independent samples, we investigated the DIB in relation to the season of birth.Results: In the Stockholm sample, those born during February to April had significantly lower CSF levels of 5-HIAA, and those born during October to January had significantly higher CSF levels of HVA, HVA/5-HIAA, and HVA/MHPG, as well as (non-significantly) higher levels of 5-HIAA. Those with an intermediate score of section II (impulse action patterns) of the DIB had significantly higher CSF levels of 5-HIAA and HVA, and they were significantly more likely to have been born during October to January. In the Västerbotten register, those born during February to April were significantly more likely to have preferred hanging rather than poisoning or petrol gases, and conversely for those born during October to January. These associations with suicide methods were found for the total sample and for those without any history of psychiatric contacts, but not for those with psychiatric contacts.Conclusions: Suicidal behaviour shows statistically significant variation according to the season of birth, most probably mediated by a variation in an independent trait of vulnerability to suicide based on neurodevelopmental parameters, particularly the serotonergic system. The suicidal process differs between those who seek psychiatric care compared to those who do not, reflecting differences in the diagnostic spectra and in the extent of mental illness.
|
|
| 4. |
- Engström, Maria, et al.
(författare)
-
Hartree-Fock linear response calculations of g-tensors of substituted benzene radicals
- 1999
-
Ingår i: Chemical Physics. - : Elsevier. - 0301-0104 .- 1873-4421. ; 243:3, s. 263-271
-
Tidskriftsartikel (refereegranskat)abstract
- Linear response theory has been applied for calculations of g-tensors of organic radicals in order to test the range of validity of restricted Hartree-Fock reference states. The g-values were calculated for the benzene cation (C6H6+), the benzene anion (C6H6-), hydropyrazine (C4H5N2), the dihydropyrazine cation (C4H6N2+), the aniline radical (C6H5NH), the p-benzoquinone anion (C6H4O2-), phenoxyl (C6H5O), the nitrobenzene anion (C6H5NO2-), and the nitropyridine anion (C5H4N2O2-). Influence of variations of structural parameters on the g-tensor components were investigated. Calculated g-values were in excellent agreement with experiment for six out of nine radicals. Two radicals - the p-benzoquinone anion and aniline radical - showed minor discrepancies, while the g-tensor of the phenoxyl radical was incorrect. The problem with the phenoxyl radical was traced to a complex electronic structure and optical spectrum. Results consistent with experiment could in that case only be obtained with electron correlated calculations.
|
|
| 5. |
- Engström, Maria, et al.
(författare)
-
Linear response calculations of electronic g-factors and spin-rotational coupling constants for diatomic molecules with a triplet ground state
- 1998
-
Ingår i: Chemical Physics. - : Elsevier. - 0301-0104 .- 1873-4421. ; 237:1-2, s. 149-158
-
Tidskriftsartikel (refereegranskat)abstract
- Electronic g-factors for ESR spectra of a number of diatomic molecules with a ground X3Σ- state and their electronic spin-rotational coupling constants have been calculated by a linear response method. General expressions are used for the second order correction to the electronic g-factor which account for spin-orbit coupling induced admixtures from all excited triplet states to the ground state orbital magnetism. First order corrections - the spin-Zeeman kinetic energy contribution and the one-electron spin-Zeeman gauge contribution - to the g-factor are also accounted for. Calculated g-factors and spin-rotational coupling constants are in a good agreement with available experimental data. In particular, the positive, anomalous, sign of the spin-rotational coupling constant of the PF radical is reproduced.
|
|
| 6. |
- Gelmukhanov, F, et al.
(författare)
-
Collapse of vibrational structure in spectra of resonant x-ray Raman scattering
- 1997
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 56:1, s. 256-264
-
Tidskriftsartikel (refereegranskat)abstract
- Extreme narrowing, or collapse, of electron-vibrational bands is predicted as a new phenomenon in resonant radiative and nonradiative x-ray scattering (RXS) spectra. It is shown that in the inelastic scattering case, that is, when the potential surfaces of ground and final slates are different, a considerable narrowing of the vibronic RXS band results from detuning the excitation Photon frequency omega away from the absorption resonance. By fine tuning the frequency, this may under special circumstances also occur in the region of strong photoabsorption. In the case of elastic Rayleigh scattering, that is, when the potential surfaces of ground and final states are identical, the narrowing results in a total collapse to a single resonance by detuning the frequency. The theory predicts how the differencies in vibrational structure of resonant and nonresonant photoemission spectra depends on the excitation frequency. The effect of frequency detuning on complex spectral multilevel structures due to multiplet: and spin-orbit splittings is discussed qualitatively. It is shown that the notion of: duration time for the x-ray scattering process plays a crucial role in the understanding of RXS spectra.
|
|
| 7. |
- Gel'mukhanov, Faris, et al.
(författare)
-
Doppler effects in resonant x-ray Raman scattering
- 1998
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 57:4, s. 2511-2526
-
Tidskriftsartikel (refereegranskat)abstract
- Theory for Doppler effects in resonant x-ray Raman scattering (RXS) is presented. It is shown that the "electron" Doppler effect is important in nonradiative RXS for decay transitions between continuum nuclear states lying above the dissociation threshold, and that the averaging of the RXS cross section over molecular orientations can lead to strong non-lorentzian broadenings of the atomiclike resonances. The Doppler effect is found to give a unique possibility to distinguish dissociating identical atoms, because different peaks correspond to atoms with opposite Doppler shifts. Spectral features of the atomiclike profile are predicted and analyzed. Strong oscillations of the RXS cross section will occur as a consequence of the interference of the Auger electrons. Due to the Doppler effect and the interference, the atomiclike profile can be associated with supernarrow spectral features, the width of which goes below the lifetime broadening and is practically independent of the spectral distribution of the incident radiation. As another consequence of the oscillations and strong anisotropy caused by the interference, we predict parity selection rules for Auger decay transitions in both bound and dissociative systems. The corresponding experiments can be realized by measurements of resonant Auger of surface adsorbed molecules and for molecules by the electron-ion coincidence technique.
|
|
| 8. |
- Gel’mukhanov, Faris, et al.
(författare)
-
Duration of x-ray Raman scattering
- 1999
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 59:1, s. 380-389
-
Tidskriftsartikel (refereegranskat)abstract
- There has recently been much interest in using the notion of a duration time to analyze resonant x-ray Raman scattering (RXS) of atoms, molecules, and solids. This notion implies a selection of processes with different time scales responsible for the formation x-ray Raman spectra, and has been useful for actual predictions of various phenomena associated with RXS and that subsequently have been experimentally verified. However, the notion of a duration time for the x-ray scattering event can also have some paradoxical consequences, as when comparing the RXS duration with the relaxation time of the wave packet evolution in the case when the inverse detuning of the excitation energy is shorter than the time of flight or the lifetime of the core excited state. We present here a solution of this contradiction and give a detailed analysis of the notion of the duration time for RXS. It is shown that this time is complex and consists of two qualitatively different contributions. The first originates in the irreversible decay of the core excited state, while the imaginary part is caused by a reversible dephasing in the time domain. We investigate also the evolution of the wave packets of bound and dissociative states to stationary distributions. The theoretical analysis is accompanied by numerical examples of the time evolution of the wave packet in bound and dissociative core excited states of the N2 and HCl molecules.
|
|
| 9. |
- Gelmukhanov, F, et al.
(författare)
-
Restoration of selection rules in nonadiabatic resonant inelastic x-ray scattering
- 1997
-
Ingår i: Journal of Experimental and Theoretical Physics. - : Pleiades Publishing Ltd. - 1063-7761 .- 1090-6509. ; 85:1, s. 20-26
-
Tidskriftsartikel (refereegranskat)abstract
- Recently a new effect in the Raman scattering of x-ray radiation has been predicted theoretically and discovered in experiments, the effect of restoration of the selection rules for the scattering tensor under strong electron-vibrational interaction. We propose a fairly simple model for describing this effect, a model that allows for an exact solution and takes into account the real vibrational structure of the molecule and electron-vibrational interaction.
|
|
| 10. |
- Gel'mukhanov, F, et al.
(författare)
-
Soft and hard x-ray Raman scattering by oriented symmetrical molecules : Selection rules, interference, and dephasing mechanisms
- 1998
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 109:12, s. 5060-5069
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant x-ray Raman scattering in chaotical, partial, and fixed oriented symmetric molecules is analyzed for x-ray photon excitation frequencies in both the soft and the hard x-ray regions. Different dephasing mechanisms and their connection with channel interference and the observation of selection rules are investigated. It is predicted that for harder x-ray energies the scattering cross sections become strongly anisotropic and oscillatory due to channel interference. The orientational dephasing is predicted to be an important coherence-blocking mechanism and can be introduced even by zero-point vibrational or librational motions. The connections between selection rules, symmetry and phase factors of the photon wave function, Bragg conditions and the channel interference show that the selection rules may operate for oriented, surface adsorbed, molecules even in the hard x-ray region. The possibility of using the interference effect for structure determination of adsorbates is discussed.
|
|
