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- Costa Felicissimo, Viviane
(författare)
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Infrared - X-ray pump probe spectroscopy
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis concerns theoretical studies of molecular interactions investigated by infrared and X-ray spectroscopic techniques, with emphasis on using the two technologies combined in pump probe experiments. Three main types of studies are addressed: the use of near-edge X-ray absorption fine structure spectra (NEXAFS) to manifest through-bond and through-space interactions; the role of hydrogen bonding on the formation of X-ray photoelectron spectra as evidenced by simulations of the water dimer; and the development of theory, with sample applications, for infrared X-ray pump probe spectroscopy - the main theme of the thesis. Ab initio calculations indicate that NEXAFS spectra give direct information about the through-bond and through-space interactions between vacant non-conjugated π* orbitals. It is found that the X-ray photoelectron spectrum of the water dimer differs strongly from the monomer spectrum in that two bands are observed, separated by the chemically shifted ionization potentials of the donor and the acceptor. The hydrogen bond is responsible for the anomalously strong broadening of these two bands. The studies show that X-ray core electron ionization of the water dimer driven by an infrared field is a proper technique to prove the proton transfered state contrary to conventional X-ray photoelectron spectroscopy. Our simulations of infrared X-ray pump-probe spectra were carried out using wave packet propagation techniques. The physical aspects of the proposed new X-ray spectroscopic method - phase sensitive Infrared - X-ray pump probe spectroscopy - are examined in detail in two sample applications - on the NO molecule and on the dynamics of proton transfer in core ionized water dimer. It is found that the phase of the infrared pump field strongly influences the trajectory of the nuclear wave packet on the ground state potential. This results in a phase dependence of the X-ray pump probe spectra. A proper choice of the delay time of the X-ray pulse allows to directly observe the X-ray transition in the proton transfered well of the core excited potential.
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- Costa Felicissimo, Viviane
(författare)
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Principles of Infrared - X-ray Pump-probe Spectroscopy
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis concerns theoretical studies of molecular interactions investigated by infrared and X-ray spectroscopic techniques, with emphasis on using these two techniques combined in pump-probe experiments. Four main types of studies are addressed: the use of near-edge X-ray absorption fine structure spectra (NEXAFS) to manifest through-bond and through-space interactions; the role of hydrogen bonding in the formation of X-ray photoelectron spectra as evidenced by simulations of the water dimer; the development of theory, with sample applications, for infrared X-ray pump-probe spectroscopy; and molecular dynamics simulations of light-induced fragmentation of water clusters.Ab initio calculations indicate that NEXAFS spectra give direct information about the through-bond and through-space interactions between vacant non-conjugated π* orbitals. It is found out that the X-ray photoelectron spectrum of the water dimer differs dramatically from the monomer spectrum in that two bands are observed, separated by the chemically shifted ionization potentials of the donor and the acceptor. The hydrogen bond is responsible for the anomalously strong broadening of these two bands. The studies show that X-ray core electron ionization of the water dimer driven by an infrared field is a proper technique to prove the proton transfered state contrary to conventional X-ray photoelectron spectroscopy.The physical aspects of the proposed new X-ray spectroscopic method - phase sensitive Infrared - X-Ray Pump-Probe Spectroscopy - are examined in detail using the wave packet technique in three applications; the NO molecule and the dynamics of proton transfer in core ionized water dimer and glyoxalmonoxime. It is found out that the phase of the infrared pump field strongly influences the trajectory of the nuclear wave packet on the ground state potential, which results in a phase dependence of the X-ray pump-probe spectra. A proper choice of the delay time of the X-ray pulse allows the direct observation of the X-ray transition in the proton transfered well of the core excited potential. It is found out that the glyoxalmonoxime molecule possesses an important feature; proton transfer accompanied by core hole hopping. Special attention is paid to the quantum control of the populations of vibrational level which is of crucial importance to shape the wave packet of desirable size.The wave packet technique becomes computationally very expensive when the number of nuclear degrees of freedom is large. Molecular dynamics is used instead in studies of light-induced nuclear kinetics in the water hexamer cluster. We predict a novel mechanism of the mechanical action of light on atoms and molecules. This mechanism is based on the rectification of the Lorentz force, which gives a unique opportunity of direct site selective mechanical action of light on atoms and molecules inside large systems like clusters or biomolecules.
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- Liu, Ji-Cai, et al.
(författare)
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Coherent control of population and pulse propagation beyond the rotating wave approximation
- 2008
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Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 41:7
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of populations of the vibrational states in a NO molecule ( one-photon absorption) and of the electronic states in a 4,4'-bis( dimethylamino) stilbene molecule ( two-photon absorption) is studied versus the frequency, intensity and shape of the laser pulse. We show that specially designed infrared laser pulses can build selective populations of certain vibrational states. A detuning of light frequency from the vibrational resonance qualitatively changes the dynamics of populations. It is found out that the populations of the nonresonant levels follow the pulse shape adiabatically if the detuning significantly exceeds the inverse characteristic time of the change of the pulse. Depopulation of the nonresonant vibrational states leads to a high population of the resonant state at the end of the pulse. Complete breakdown of the standard rotating wave approximation for a two-photon absorption process is observed even for a rather small intensity of the laser pulse. An analytical solution for the interaction of a pulse with a three-level system beyond the rotating wave approximation is obtained, and it is in close agreement with the strict numerical solution of the amplitude equations. Special attention is paid to the population dynamics of randomly oriented molecules. The orientational disorder as well as the vibrations limit the coherent population transfer. Calculations show the strong role of the anisotropy of photoexcitation in the coherent control of populations which can affect the anisotropy of photobleaching.
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- Tu, Yaoquan, et al.
(författare)
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Mechanical action of infrared light on atoms and molecules through a rectification of the electric force
- 2009
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 80:5
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Tidskriftsartikel (refereegranskat)abstract
- We report the mechanical action of infrared light on atoms and molecules based on the rectification of the electric force. This mechanism is qualitatively different from the conventional ways of controlling photochemistry. The rectification of the electric force originates from the synchronous charge transfer induced by the laser field. This brings about an opportunity to produce a site selective light-induced action, controlled by the tailored intense laser field, on atoms in molecules and clusters. The concept is illustrated by ab initio molecular dynamics simulations of the water hexamer.
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