Quantum dynamics of physicochemical processes in superfluid (4)He nanodroplets
The present thesis presents several theoretical studies on the dynamical processes of physicochemical interest involving superfluid helium (4He) nanodroplets. It has been developed a theoretical approach and computationally implemented. This consists in the first stage on the theoretical study of ch...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2015 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/313040 |
| Acceso en línea: | http://hdl.handle.net/10803/313040 |
| Access Level: | acceso abierto |
| Palabra clave: | Nanoquímica Nanochemistry Heli líquid Helio líquido Liquid helium Reaccions químiques Reacciones químicas Chemical reactions Transferència d'energia Transferencia de energía Energy transfer Líquids quàntics Líquidos cuánticos Quantum liquids Ciències Experimentals i Matemàtiques 544 |
| Sumario: | The present thesis presents several theoretical studies on the dynamical processes of physicochemical interest involving superfluid helium (4He) nanodroplets. It has been developed a theoretical approach and computationally implemented. This consists in the first stage on the theoretical study of chemical reaction dynamics in superfluid helium nanodroplets. The description of the system is fully quantum and consists in a hybrid method in which different theoretical approaches are combined to describe the different components of the system. The liquid helium (superfluid) has been described through the Density Functional Theory (DFT), using a phenomenological energy functional. Atomic and molecular impurities have been described by means of standard quantum dynamics. The methodology developed in the present thesis has been applied to the study of various physicochemical processes of interest. These studies con be grouped as: - Study of the structure, energy and electronic spectroscopy of helium nanodroplets doped with atomic oxygen in different electronic states. In this work, the influence of the electronic state of oxygen and energy structure of the drop has been determined to be the induction of anisotropy on the helium density (for the open-shell cases), as well as the high quality of helium nanodroplets acting as a matrix for high-resolution spectroscopy confirmed. - Investigation on the dynamics of the photodissociation of homonuclear diatomic molecules in superfluid helium nanodroplets. In this context, the method developed has been initially applied to the case of molecular chlorine. Some interesting results related with the energy exchange phenomenon and generation of quantum (confined) resonances due tot the interaction of the molecules with the helium nanodroplet have been reported. Moreover, the relaxation process of the nanodroplet after the photodissociation has been also studied. This methodology developed has been also applied to the case of two halogen homonuclear diatomic molecules more, Br2 and I2. Different phenomenology and mechanism have been found for these cases, even producing full recombination for the biggest droplet considered. Furthermore, in order to determine the role played by the mass of the atoms of the diatomic homonuclear molecule on this process, we have studied the photodissociation dynamics of prototypic “isomers” of Cl2. - We have modeled the process of the capture of a neon atom by superfluid helium nanodroplets. We have restricted to the case of zero angular momentum as a first approach to the problem at the quantum level. We obtained the time scale of this process. Also, it was found that the energy exchange does not take place at any time, but until the velocity is low enough (Landau’s critical velocity) there is no mechanism for the exchange energy. This leads to a constant (mean) velocity of the quantum particle (Ne atom), since the friction force is zero. The resulting wave packet in momentum representation has a Gaussian type profile. - The synthesis reaction of a dimer of van der Waals (Ne2) in helium nanodroplets has been investigated. This process starts with a drop initially doped with Ne atom. Then, a second Ne atom is captured, which initiates the process of the synthesis. We have restricted to the zero angular momentum case for computational reasons. A great variety of phenomenology (reaction mechanisms) depending on the collision velocity and the droplet size has been found. |
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