| 1. |
- Felicissimo, Viviane, et al.
(författare)
-
A theoretical study of the role of the hydrogen bond on core ionization of the water dimer
- 2005
-
Ingår i: Chemical Physics. - : Elsevier. - 0301-0104 .- 1873-4421. ; 312:1-3, s. 311-318
-
Tidskriftsartikel (refereegranskat)abstract
- Motivated by the interest in using X-ray spectra for probing of hydrogen bonded networks we developed a quantum model for simulations of the electronic-vibrational profile of the X-ray core photoelectron spectrum of the water dimer. It is found that the potential surfaces of the donor and acceptor O1s core-ionized states of this system display a qualitative difference. Large gradients of the potential in the core ionized state along some intermolecular coordinates combined with small vibrational frequencies breaks down completely the harmonic approximation. The band profiles are therefore treated using a quasi-continuum approximation. The weak hydrogen bonding and the drastic change of water dimer potential under core ionization is responsible for the anomalously strong vibrational broadening: 0.4 eV for the acceptor band and 0.6 eV for the donor band. The core ionization of the donor oxygen is accompanied by proton transfer which should be observable in X-ray fluorescence or Auger spectra.
|
|
| 2. |
- Felicissimo, Viviane C., et al.
(författare)
-
Enhancement of the recoil effect in x-ray photoelectron spectra of molecules driven by a strong ir field
- 2005
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:2, s. 023414-
-
Tidskriftsartikel (refereegranskat)abstract
- The C K and O K x-ray photoelectron spectra of the CO molecule, driven by a strong ir field, are studied theoretically. An enhancement of the recoil effect, which results in a strong dependence of the electron vibrational profile on the energy of x-ray photon, is found. The enhancement of the recoil effect happens due to an ir-induced increase of the wave-packet size. An extra enhancement occurs when the gradients of ground and ionized states approach each other. Under an increase of the photon energy, different sides of the x-ray photoelectron band experience blue- and redshifts, which are related to the difference of the gradients of the ground and core ionized states in the points of the vertical transitions near turning points of the wave packet. This makes the ir-x-ray pump-probe spectroscopy a very promising tool to study the shape of the potential energy surfaces.
|
|
| 3. |
- Felicissimo, Viviane C., et al.
(författare)
-
The principles of infrared-x-ray pump-probe spectroscopy. Applications on proton transfer in core-ionized water dimers
- 2005
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 122:9
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we derive the basic physics underlying infrared-x-ray pump-probe spectroscopy (IR, infrared). Particular features of the spectroscopy are highlighted and discussed, such as dependence on phase of the infrared pulse, duration and delay time of the x-ray pulse, and molecular orientation. Numerical applications are carried out for the water dimer using wave packet techniques. It is shown that core ionization of the donor oxygen of the water dimer results in a drastic change of the potential with the global minimum placed in the proton transfer region. The results of the modeling indicate that IR-x-ray pump-probe spectroscopy can be used to study the dynamics of proton transfer in this core-ionized state, and that, contrary to conventional core level photoelectron spectroscopy, x-ray core-ionization driven by an IR field is a proper method to explore the proton transfer in a system like the water dimer. We observe that the trajectory of the nuclear wave packet in the ground state potential well is strongly affected by the absolute phase of the IR pulse.
|
|
| 4. |
- Guimaraes, Freddy Fernandes, et al.
(författare)
-
Infrared–x-ray pump-probe spectroscopy of the NO molecule
- 2005
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:1
-
Tidskriftsartikel (refereegranskat)abstract
- Two color infrared-x-ray pump-probe spectroscopy of the NO molecule is studied theoretically and numerically in order to obtain a deeper insight of the underlying physics and of the potential of this suggested technology. From the theoretical investigation a number of conclusions could be drawn: It is found that the phase of the infrared field strongly influences the trajectory of the nuclear wave packet, and hence, the x-ray spectrum. The trajectory experiences fast oscillations with the vibrational frequency with a modulation due to the anharmonicity of the potential. The dependences of the x-ray spectra on the delay time, the duration, and the shape of the pulses are studied in detail. It is shown that the x-ray spectrum keep memory about the infrared phase after the pump field left the system. This memory effect is sensitive to the time of switching-off the pump field and the Rabi frequency. The phase effect takes maximum value when the duration of the x-ray pulse is one-fourth of the infrared field period, and can be enhanced by a proper control of the duration and intensity of the pump pulse. The manifestation of the phase is different for oriented and disordered molecules and depends strongly on the intensity of the pump radiation.
|
|
| 5. |
- Guimaraes, Freddy Fernandes, et al.
(författare)
-
Phase sensitive x-ray absorption driven by strong infrared fields
- 2005
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 71:4
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper it is demonstrated that electron vibrational absorption of molecules driven by strong IR field provides rich physical interpretations of dynamical processes on a short time scale. The phase of an infrared field influences strongly the trajectory of the nuclear wave packet and the probing spectrum. It is shown that the probe spectrum keeps memory of the infrared phase even after that the pump field left the system. The phase effect takes maximum value when the duration of the probe pulse is of the order of the infrared field period, and can be enhanced by a proper control of the duration and intensity of the pump pulse. The phase effect is different for oriented and disordered molecules and depends strongly on the intensity of pump radiation. It can be an effective tool to study charge transfer processes like proton transfer in hydrogen bonded networks.
|
|
| 6. |
- Guimaraes, Freddy Fernandes, et al.
(författare)
-
Pump-probe spectroscopy of molecules driven by infrared field in both ground and excited electronic states
- 2006
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 125:20
-
Tidskriftsartikel (refereegranskat)abstract
- Pump-probe spectra of molecules driven by strong infrared (IR) field in both ground and excited states are studied theoretically. The role of the final state interaction becomes important when pump and probe pulses overlap, and the Rabi frequency is comparable with the lifetime broadening of the excited state and the duration of the pump pulse. Our theoretical approach is applied to x-ray absorption of nitrogen molecule and valence photoionization of carbon monoxide. It is shown that IR-x-ray pump-probe spectroscopy can directly evidence the delocalization of core hole.
|
|
| 7. |
- Guimaraes, Freddy Fernandes, et al.
(författare)
-
Quantum wave packet revivals in IR plus X-ray pump-probe spectroscopy
- 2005
-
Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 405:4-6, s. 398-403
-
Tidskriftsartikel (refereegranskat)abstract
- The wave packet revivals constitute a central concept of X-ray spectroscopy with ultra-high spectral resolution. The revival phenomenon allows to resolve the anharmonical shift or rotational structure by means of time dependent measurements and makes X-ray pump-probe spectroscopy a powerful technique to study long-term dynamics of molecules in different phases. We study the revivals referring to the X-ray absorption spectrum of the NO molecule driven by strong infrared pulse. It is shown that the phase sensitive trajectories of the center of gravity of the wave packets and the X-ray spectra copy each other.
|
|
| 8. |
- Guimaraes, Freddy Fernandes, 1975-
(författare)
-
X-ray Spectroscopy of Molecules Driven by Strong IR Fields
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current thesis deals with one important branch of the physics of ultrafast processes, namely modeling of femtosecond nuclear dynamics. We suggest a new type of time resolved spectroscopy, the phase sensitive infrared-x-ray pump probe spectroscopy, which combines rich opportunities of IR laser techniques in quantum control of molecular systems with the site selectivity of x-rays. We have developed and applied a dynamical theory of x-ray pump-probe spectroscopy to study different molecular systems. Special attention is paid to design of the wave packets of desirable shape and spectral composition. Such a quantum control of the nuclear wave packet enables the study of molecular properties in regions that are unavailable by standard x-ray spectroscopies. The IR - x-ray pump probe spectroscopy is nicely suited to perform mapping of wave packet trajectories, to study revival phenomena, femtosecond chemical dynamics, and proton transfer, to mention a few examples. Our simulations show that the phase of the infrared pulse strongly influences the trajectory of the nuclear wave packet, and hence, the x-ray spectrum. Such a dependence is caused by the transfer of the phase of the IR field to the wave packet through the interference of the one (x-ray) and two-photon (IR + x-ray) excitation channels. The time resolved x-ray spectra are sensitive to the shape, duration and delay time between the pulses. The phase of the IR pulse influences the molecular dynamics also when the Rabi period becomes comparable with the period of vibrations, breaking down the rotating wave approximation. We predict a phase memory effect which is a promising technique in studies of chemical dynamics on different time scales. It is shown that the final state interaction with the pump affects the probe spectrum when the pump and probe pulses overlap. In a further step, we explore the electronic recoil effect in x-ray photoelectron spectroscopy, which has recently attracted attention of experimentalists due to its sensitivity to intramolecular interaction. We show that an IR field enhances the manifestation of the recoil effect through the formation of extensive vibrational wave packets. The theory of x-ray Raman scattering from molecules with strong spin-orbit coupling accompanied by electron-hole interaction is developed and applied to simulations of resonant x-ray Raman scattering of the HCl molecule. Special attention is paid to the theoretical methodologies to reduce the computational cost of our wave packet codes.
|
|
| 9. |
- Kimberg, Victor, et al.
(författare)
-
Phase-sensitive wave-packet dynamics caused by a breakdown of the rotating-wave approximation
- 2006
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 73:2
-
Tidskriftsartikel (refereegranskat)abstract
- The water dimer driven by strong infrared field is studied in the two-vibrational mode approximation. A pump pulse excites the OH vibrational modes and creates a coherent superposition of vibrational states of the low-frequency OO mode. The solution of the Schrodinger equation in the adiabatic approximation shows a strong sensitivity of the OO vibrational wave-packet dynamics to the absolute phase of the pump field. This effect appears due to a break down of the rotating-wave approximation when the Rabi frequency of the OH vibrational transition approaches the frequency of the OH mode. The violation of the rotating wave approximation modifies considerably the interaction of the probe radiation with the laser-driven molecule.
|
|
| 10. |
- Liu, Ji-Cai, et al.
(författare)
-
Coherent control of population and pulse propagation beyond the rotating wave approximation
- 2008
-
Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 41:7
-
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.
|
|
| 11. |
- Såthe, C., et al.
(författare)
-
Resonant LII;III x-ray raman scattering from HCl
- 2006
-
Ingår i: Physical Review A. - 1050-2947 .- 1094-1622. ; 74:6, s. 062512-
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied the spectral features of Cl LII,III resonant x-ray Raman scattering of HCl molecules in gas phase both experimentally and theoretically. The theory, formulated in the intermediate-coupling scheme, takes into account the spin-orbital and molecular-field splittings in the Cl 2p shells, as well as the Coulomb interaction of the core hole with unoccupied molecular orbitals. Experiment and theory display nondispersive dissociative peaks formed by decay transitions in both molecular and dissociative regions. The molecular and atomic peaks collapse in a single narrow resonance because the dissociative potentials of core-excited and final states are parallel to each other along the whole pathway of the nuclear wave packet.
|
|
| 12. |
- Tu, Yaoquan, et al.
(författare)
-
Mechanical action of infrared light on atoms and molecules through a rectification of the electric force
- 2009
-
Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 80:5
-
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.
|
|
