IQ - Artigos publicados em periódicos
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Navegando IQ - Artigos publicados em periódicos por Autor "Ågren, Hans"
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Item A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering(2017-03-14) Cruz, Vinícius Vaz da; Ertan, Emelie; Couto, Rafael Carvalho; Eckert, Sebastian; Fondell, Mattis; Dantz, Marcus; Kennedy, Brian; Schmitt, Thorsten; Pietzsch, Annette; Guimarães, Freddy Fernandes; Ågren, HansIn this combined theoretical and experimental study we report a full analysis of the resonant inelastic X-ray scattering (RIXS) spectra of H2O, D2O and HDO. We demonstrate that electronically-elastic RIXS has an inherent capability to map the potential energy surface and to perform vibrational analysis of the electronic ground state in multimode systems. We show that the control and selection of vibrational excitation can be performed by tuning the X-ray frequency across core-excited molecular bands and that this is clearly reflected in the RIXS spectra. Using high level ab initio electronic structure and quantum nuclear wave packet calculations together with high resolution RIXS measurements, we discuss in detail the mode coupling, mode localization and anharmonicity in the studied systems.Item Gradual collapse of nuclear wave functions regulated by frequency tuned X-ray scattering(2017) Ignatova, Nina; Cruz, Vinícius Vaz da; Couto, Rafael Carvalho; Zimin, Andrey; Guimarães, Freddy Fernandes; Polyutov, Sergey; Ågren, Hans; Kimberg, Victor; Odelius, Michael; Gel’mukhanov, FarisAs is well established, the symmetry breaking by isotope substitution in the water molecule results in localisation of the vibrations along one of the two bonds in the ground state. In this study we find that this localisation may be broken in excited electronic states. Contrary to the ground state, the stretching vibrations of HDO are delocalised in the bound core-excited state in spite of the mass difference between hydrogen and deuterium. The reason for this effect can be traced to the narrow “canyon-like” shape of the potential of the state along the symmetric stretching mode, which dominates over the localisation mass-difference effect. In contrast, the localisation of nuclear motion to one of the HDO bonds is preserved in the dissociative core-excited state . The dynamics of the delocalisation of nuclear motion in these core-excited states is studied using resonant inelastic X-ray scattering of the vibrationally excited HDO molecule. The results shed light on the process of a wave function collapse. After core-excitation into the state of HDO the initial wave packet collapses gradually, rather than instantaneously, to a single vibrational eigenstate.Item Infrared-pump–x-ray-probe spectroscopy of vibrationally excited molecules(2017) Ignatova, Nina; Cruz, Vinícius Vaz da; Couto, Rafael Carvalho; Ertan, Emilie; Odelius, Michael; Ågren, Hans; Guimarães, Freddy Fernandes; Zimin, Andrei; Polyutov, Sergey P.; Gel'mukhanov, Faris; Kimberg, VictorWe develop a theory of infrared (IR)-pump–x-ray-probe spectroscopy for molecular studies. We illustrate advantages of the proposed scheme by means of numerical simulations employing a vibrational wave packet technique applied to x-ray absorption and resonant inelastic x-ray scattering (RIXS) spectra of the water molecule vibrationally excited by a preceding IR field. The promotion of the vibrationally excited molecule to the dissociative 1a−1 1 4a1 and bound 1a−1 1 2b2 core-excited states with qualitatively different shapes of the potential energy surfaces creates nuclear wave packets localized along and between the OH bonds, respectively. The projection of these wave packets on the final vibrational states, governed by selection and propensity rules, results in spatial selectivity of RIXS sensitive to the initial vibrationally excited state, which makes it possible to probe selectively the ground state properties along different modes. In addition, we propose to use RIXS as a tool to study x-ray absorption from a selected vibrational level of the ground state when the spectral resolution is sufficiently high to resolve vibrational overtones. The proposed technique has potential applications for advanced mapping of multidimensional potential energy surfaces of ground and core-excited molecular states, for symmetry-resolved spectroscopy, and for steering chemical reactions.